Tetrhydropyridoindole Derivatives

ABSTRACT

The invention relates to tetrahydropyridoindole derivatives and their use as active ingredients in the preparation of pharmaceutical compositions. The invention also concerns related aspects including processes for the preparation of the compounds, pharmaceutical compositions comprising one or more of those compounds and methods of treatment comprising administration of said compounds.

This application is a divisional of U.S. patent application Ser. No. 10/598,777, filed Sep. 11, 2006, which is a national stage of PCT/EP2005/002362, filed Mar. 7, 2005, the subject matter of which is incorporated herein. This application further claims priority to EP 04002493, filed Mar. 11, 2004, the subject matter of which is incorporated herein.

FIELD OF THE INVENTION

The present invention relates to novel tetrahydropyridoindole derivatives and their use as potent CRTH2 receptor antagonists in the treatment of prostaglandin mediated diseases, to pharmaceutical compositions comprising these derivatives and to processes for their preparation. In particular, such derivatives may be used alone or in pharmaceutical compositions for the treatment of both chronic and acute allergic/immune disorders such as allergic asthma, rhinitis, chronic obstructive pulmonary disease (COPD), dermatitis, inflammatory bowel disease, rheumatoid arthritis, allergic nephritis, conjunctivitis, atopic dermatitis, bronchial asthma, food allergy, systemic mast cell disorders, anaphylactic shock, urticaria, eczema, itching, inflammation, ischemia-reperfusion injury, cerebrovascular disorders, pleuritis, ulcerative colitis, eosinophil-related diseases, such as Churg-Strauss syndrome and sinusitis, basophil-related diseases, such as basophilic leukemia and basophilic leukocytosis in humans and other mammals.

BACKGROUND OF THE INVENTION

Prostaglandin D2 is a known agonist of the thromboxane A2 (TxA2) receptor, the PGD2 (DP) receptor and the recently identified G-protein-coupled “chemoattractant receptor-homologous molecule expressed on Th2 cells” (CRTH2).

The response to allergen exposure in a previously sensitized host results in a cascade effect involving numerous cell types and release of a number of cytokines, chemokines, and multiple mediators. Among these critical initiators are the cytokines interleukin (IL)-4, IL-13, and IL-5, which play critical roles in Th2 cell differentiation, immunoglobulin (Ig)E synthesis, mast cell growth and differentiation, upregulation of CD23 expression, and the differentiation, recruitment, and activation of eosinophils. The stimulated release of the array of mediators, causes end-organ damage, including constriction and hyperresponsiveness, vascular permeability, edema, mucous secretion, and further inflammation.

Because of the number of responses targeted, corticosteroids have proven to be the most effective therapy. Rather than antagonizing these specific responses in a directed way, another approach is to alter the immune response, that is, to change the nature of the immunological response to allergen. CRTH2 is preferentially expressed on Th2 cells and is a chemoattractant receptor for PGD2 that mediates PGD2-dependent migration of blood Th2 cells. Chemoattractants are responsible for the recruitment of both Th2 cells and other effector cells of allergic inflammation, which can provide the conceptual basis for the development of new therapeutic strategies in allergic conditions.

So far, few compounds having CRTH2 antagonistic activity have been reported in the patent literature. Bayer AG claims the use of Ramatroban ((3R)-3-(4-fluorobenzene-sulfonamido)-1,2,3,4-tetrahydrocarbazole-9-propi-onic acid) for the prophylaxis and treatment of allergic diseases, such as asthma, allergic rhinitis or allergic conjuvatitis (GB 2388540). Further, (2-tert.-butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-aceti-c acid and (2-ethoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-a-cetic acid are disclosed by Kyle F. et al in two patent applications (U.S. Pat. No. 5,817,756 and WO 9507294, respectively).

Furthermore, oral bioavailability of the Ramatroban and its ability to inhibit prostaglandin D2-induced eosinophil migration in vitro has been reported (Journal of Pharmacology and Experimental Therapeutics, 305(1), p. 347-352 (2003)).

DESCRIPTION OF THE INVENTION

It has now been found that compounds of the general Formulae (I) and (II) of the present invention are CRTH2 receptor antagonists. These compounds are useful for the treatment of both chronic and acute allergic/immune disorders such as allergic asthma, rhinitis, chronic obstructive pulmonary disease (COPD), dermatitis, inflammatory bowel disease, rheumatoid arthritis, allergic nephritis, conjunctivitis, atopic dermatitis, bronchial asthma, food allergy, systemic mast cell disorders, anaphylactic shock, urticaria, eczema, itching, inflammation, ischemia-reperfusion injury, cerebrovascular disorders, pleuritis, ulcerative colitis, eosinophil-related diseases, such as Churg-Strauss syndrome and siniusitis, basophil-related diseases, such as basophilic leukemia and basophilic leukocytosis.

The following paragraphs provide definitions of the various chemical moieties that make up the compounds according to the invention and are intended to apply uniformly throughout the specification and claims unless an otherwise expressly set out definition provides a broader definition.

The term “C₁-C₅-alkyl”, alone or in combination with other groups, means a straight-chain or branched-chain alkyl group with 1-5 carbon atoms as for example methyl, ethyl, propyl, isopropyl, butyl, sec.-butyl, tert.-butyl, isobutyl and the isomeric pentyls. Preferred are groups with 1 to 3 carbon atoms. This C₁-C₅-alkyl group may optionally be substituted by one to three substituents independently selected from cyano, halogen, hydroxy, cycloalkyl, aryl, C₂-C₅-alkenyl, C₁-C₅-alkoxy, C₂-C₅-alkenyloxy, trifluoromethyl, trifluoromethoxy, amino and carboxy. If C₁-C₅-alkyl is substituted, it preferably represents trifluoromethyl.

The term “C₀-C₅-alkyl-carbonyl”, alone or in combination with other groups, means an R—CO— group, wherein R is hydrogen or a C₁-C₅-alkyl group as defined above; examples are formyl, acetyl, propionyl, butyryl, isobutyryl and the like.

The term “C₂-C₅-alkenyl-carbonyl”, alone or in combination with other groups, means an R′—CO— group, wherein R′ is a straight-chain or branched-chain alkenyl group with 2 to 5 carbon atoms; examples are acryl, methacryl, crotonoyl and dimethylacryl.

The term “C₁-C₅-alkyl-carbamoyl”, alone or in combination with other groups, means an R″—NH—CO— group wherein R″ is a C₁-C₅-alkyl group as defined above; examples are methylcarbamoyl, ethylcarbamoyl, propylcarbamoyl, isopropylcarbamoyl, butylcarbamoyl, tert.-butylcarbamoyl and the like.

The term “C₁-C₅-alkoxy”, alone or in combination with other groups, means a group of the Formula R″—O— in which R″ is a C₁-C₅-alkyl group as defined above; examples are methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy and tert.-butoxy, preferably methoxy and ethoxy.

The term “aryl”, alone or in combination with other groups, means an aromatic carbocyclic group from 6 to 14 carbon atoms having a single ring or multiple condensed rings wherein said ring(s) is/are optionally substituted by one or more substituents independently selected from the group consisting of oxo, cyano, halogen, hydroxy, C₁-C₅-alkyl, C₂-C₅-alkenyl, C₁-C₅-alkoxy, C₂-C₅-alkenyloxy, cycloalkyl, aryl, heteroaryl, trifluoromethyl, trifluoromethoxy, amino and carboxy. Preferred aryl include phenyl or naphthyl which to optionally carry one or more substituents, preferably one or two substituents, each independently selected from cyano, halogen, hydroxy, C₁-C₅-alkyl, C₂-C₅-alkenyl, C₁-C₅-alkoxy, C₂-C₅-alkenyloxy, cycloalkyl, aryl, heteroaryl, trifluoromethyl, trifluoromethoxy, amino and carboxy.

The term “aryl-C₁-C₅-alkyl”, alone or in combination with other groups, means a C₁-C₅-alkyl group having an aryl substituent in which the aryl group is as defined above.

The term “aryl-carbonyl”, alone or in combination with other groups, means a group of the Formula Ar—CO— in which Ar is an aryl group as defined above; examples are phenyl-carbonyl and naphthyl-carbonyl.

The term “aryl-C₁-C₅-alkyl-carbonyl”, alone or in combination with other groups, means a C₁-C₅-alkyl-carbonyl group having an aryl substituent in which the aryl group is as defined above.

The term “aryl-C₁-C₅-alkoxy-carbonyl”, alone or in combination with other groups, means a C₁-C₅-alkoxy-carbonyl group having an aryl substituent in which the aryl group is as defined above.

The term “aryl-carbamoyl”, alone or in combination with other groups, means a group of the Formula Ar—NH—CO— in which Ar is an aryl group as defined above.

The term “aryl-thiocarbamoyl”, alone or in combination with other groups, means a group of the Formula Ar—NH—C(═S)— in which Ar is an aryl group as defined above.

The term “aryl-C₁-C₅-alkyl-carbamoyl”, alone or in combination with other groups, means a group of the Formula Ar—C₁-C₅-alkyl-NH—CO— in which Ar is an aryl group as defined above.

The term “aryl-C₁-C₅-alkyl-thiocarbamoyl”, alone or in combination with other groups, means a group of the Formula Ar—C₁-C₅-alkyl-NH—C(═S)— in which Ar is an aryl group as defined above.

The term “cycloalkyl”, alone or in combination with other groups, means a saturated cyclic hydrocarbon moiety containing 3-15, preferably 3-6, carbon atoms, optionally substituted by one or more groups, each individually and independently selected from C₂-C₅-alkenyl, C₁-C₅-alkoxy, C₁-C₅-alkoxy-C₁-C₅-alkyl, C₁-C₅-alkoxy-carbonyl, C₁-C₅-alkoxy-carbonyl-C₁-C₅-alkyl, C₁-C₅-alkyl, C₀-C₅-alkyl-carbonyl, C₀-C₅-alkyl-carbonyl-C₁-C₅-alkyl, C₁-C₅-alkyl-carbonyloxy, C₁-C₅-alkylendioxy, C₁-C₅-alkylsulfinyl, C₁-C₅-alkylsulfinyl-C₁-C₅-alkyl, C₁-C₅-alkylsulfonyl, C₁-C₅-alkylsulfonyl-C₁-C₅-alkyl, C₁-C₅-alkylthio, C₁-C₅-alkylthio-C₁-C₅-alkyl, C₂-C₅-alkynyl, amino, amino-C₁-C₅-alkyl, aminocarbonyl, aminocarbonyl-C₁-C₅-alkyl, aryl, aryl-C₂-C₅-alkenyl, aryl-C₁-C₅-alkoxy, aryl-C₁-C₅-alkyl, aryloxy, aryloxycarbonyl, aryloxycarbonyl-C₁-C₅-alkyl, arylsulfinyl, arylsulfinyl-C₁-C₅-alkyl, arylsulfonyl, arylsulfonyl-C₁-C₅-alkyl, arylthio, arylthio-C₁-C₅-alkyl, carboxy, carboxy-C₁-C₅-alkyl, cyano, cyano-C₁-C₅-alkyl, formyl, formyl-C₁-C₅-alkyl, halogen, haloalkoxy, halo-C₁-C₅-alkyl, hydroxy, hydroxyl-C₁-C₅-alkyl, mercapto, and nitro. Preferably, cycloalkyl is unsubstituted. Representative examples of cycloalkyl include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl, preferably cyclopropyl, cyclopentyl and cyclohexyl. In polycyclic cycloalkyl groups one of the distal rings may be aromatic, e.g., 1-indanyl, 2-indanyl, tetrahydronaphthalene, and the like.

The term “cycloalkyl-carbonyl”, alone or in combination with other groups, means a carbonyl group having a cycloalkyl substituent in which the cycloalkyl group is as defined above.

The term “cycloalkyl-C₁-C₅-alkyl-carbonyl”, alone or in combination with other groups, to means a C₁-C₅-alkyl-carbonyl group having a cycloalkyl substituent in which the cycloalkyl group is as defined above.

The term “cycloalkyl-C₁-C₅-alkoxy-carbonyl”, alone or in combination with other groups, means a C₁-C₅-alkoxy-carbonyl group having a cycloalkyl substituent in which the cycloalkyl group is as defined above.

The term “cycloalkyl-carbamoyl”, alone or in combination with other groups, means a group of the Formula cycloalkyl-NH—C(═S)— wherein the cycloalkyl group is as defined above.

The term “heteroaryl” means a monocyclic heteroaromatic, or a bicyclic or (less preferred) a tricyclic fused-ring heteroaromatic group having preferably 5 to 14, especially 5 to 10 ring members of which 1 to 3, especially 1 or 2, are heteroatoms selected from the group consisting of oxygen, nitrogen and sulphur, while the remaining ring members are carbon atoms. Heteroaryl is optionally substituted by one or more substituents, preferably one or two substituents, each independently selected from cyano, halogen, hydroxy, C₁-C₅-alkyl, C₂-C₅-alkenyl, C₁-C₅-alkoxy, C₂-C₅-alkenyloxy, cycloalkyl, aryl, heteroaryl, trifluoromethyl, trifluoromethoxy, amino and carboxy. Particular examples of heteroaromatic groups include pyridyl, pyrazinyl, pyrrolyl, furyl, thienyl, imidazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, pyrazolyl, 1,2,3-triazolyl, 1,2,4-triazolyl, 1,2,3-oxadiazolyl, 1,2,4-oxadia-zolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazoly-1,1,3,4-triazinyl, 1,2,3-triazinyl, benzofuryl, [2,3-dihydro]benzofuryl, isobenzofuryl, benzothienyl, benzotriazolyl, isobenzothienyl, indolyl, isoindolyl, 3H-indolyl, benzimidazolyl, imidazo[1,2-a]pyridyl, benzothiazolyl, benzoxa-zolyl, quinolizinyl, quinazolinyl, phthalazinyl, quinoxalinyl, cinnolinyl, naphthyridinyl, pyrido[3,4-b]pyridyl, pyrido[3,2-b]pyridyl, pyrido[4,3-b]pyridyl, quinolyl, isoquinolyl, tetrazolyl, purinyl, pteridinyl, carbazolyl, xanthenyl or benzoquinolyl. Preferred heteroaryl groups include thienyl, pyridyl or furyl, wherein said groups optionally carry one or more substituents, preferably one or two substituents, each independently selected from cyano, halogen, hydroxy, C₁-C₅-alkyl, C₂-C₅-alkenyl, C₁-C₅-alkoxy, C₂-C₅-alkenyloxy, cycloalkyl, aryl, heteroaryl, trifluoromethyl, trifluoromethoxy, amino and carboxy.

The term “heteroaryl-C₁-C₅-alkyl”, alone or in combination with other groups, means a C₁-C₅-alkyl group having a heteroaryl substituent in which the heteroaryl group is as defined above.

The term “heteroaryl-carbonyl”, alone or in combination with other groups, means a group of the Formula Het-CO— in which Het is a heteroaryl group as defined above.

The term “heteroaryl-C₁-C₅-alkyl-carbonyl”, alone or in combination with other groups, means a group of the Formula Het-C₁-C₅-alkyl-CO— in which Het is a heteroaryl group as defined above.

The term “heteroaryl-C₁-C₅-alkoxy-carbonyl”, alone or in combination with other groups, means a group of the Formula Het-C₁-C₅-alkoxy-CO— in which Het is a heteroaryl group as defined above.

The term “halogen” means fluorine, chlorine, bromine or iodine, preferably fluorine, chlorine and bromine.

Salt-forming groups are groups or radicals having basic or acidic properties. Compounds having at least one basic group or at least one basic radical, for example amino, a secondary amino group not forming a peptide bond or a pyridyl radical, may form acid addition salts, for example with inorganic acids. When several basic groups are present mono- or poly-acid addition salts may be formed.

Compounds having acidic groups, such as a carboxy group or a phenolic hydroxy group, may form metal or ammonium salts, such as alkali metal or alkaline earth metal salts, for example sodium, potassium, magnesium or calcium salts, or ammonium salts with ammonia or suitable organic amines, such as tertiary monoamines, for example triethylamine or tri-(2-hydroxyethyl)-amine, or heterocyclic bases, for example N-ethyl-piperidine or N,N′-dimethylpiperazine. Mixtures of salts are possible.

Compounds having both acidic and basic groups can form internal salts.

For the purposes of isolation or purification, as well as in the case of compounds that are used further as intermediates, it is also possible to use pharmaceutically unacceptable salts, e.g. the picrates. Only pharmaceutically acceptable, non-toxic salts may be used for therapeutic purposes, however, and those salts are therefore preferred.

The expression “pharmaceutically acceptable salts” encompasses either salts with inorganic acids or organic acids like hydrochloric or hydrobromic acid, sulfuric acid, phosphoric acid, citric acid, formic acid, acetic acid, maleic acid, tartaric acid, benzoic acid, methanesulfonic acid, p-toluenesulfonic acid, and the like that are non-toxic to living organisms. In case the compound of general Formula (I) is acidic in nature the expression encompasses salts with an inorganic base like an alkali or earth alkali base, e.g. sodium hydroxide, potassium hydroxide, calcium hydroxide, and the like which are also non-toxic to living organisms.

A first aspect of the present invention relates to novel tetrahydropyridoindole derivatives of the general Formula (I):

wherein R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₅-alkoxy, halogen, nitro, cyano or formyl; and R⁵ represents C₀-C₅-alkyl-carbonyl, C₂-C₅-alkenyl-carbonyl, C₁-C₅-alkoxy-carbonyl, C₁-C₅-alkyl, C₁-C₅-alkyl-carbamoyl, aryl-C₁-C₅-alkyl, aryl-carbonyl, aryl-C₁-C₅-alkyl-carbonyl, aryl-C₁-C₅alkoxy-carbonyl, aryl-carbamoyl, aryl-thiocarbamoyl, aryl-C₁-C₅-alkyl-carbamoyl, aryl-C₁-C₅-alkyl-thiocarbamoyl, cycloalkyl-carbonyl, cycloalkyl-C₁-C₅-alkyl-carbonyl, cycloalkyl-C₁-C₅-alkoxy-carbonyl, cycloalkyl-carbamoyl, heteroaryl-C₁-C₅-alkyl, heteroaryl-carbonyl, heteroaryl-C₁-C₅-alkyl-carbonyl or heteroaryl-C₁-C₅-alkoxy-carbonyl; with the proviso that when R¹, R², R³ and R⁴ represent hydrogen, R⁵ is not an ethoxy-carbonyl group or a tert.-butoxycarbonyl group; and optically pure enantiomers, mixtures of enantiomers, racemates, optically pure diastereoisomers, mixtures of diastereoisomers, diastereoisomeric racemates, mixtures of diastereoisomeric racemates, meso forms, and salts thereof.

The present invention also relates to tetrahydropyridoindole derivatives of the general Formula (I), wherein

R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₅-alkoxy, halogen, nitro, cyano or formyl; and R⁵ represents C₀-C₅-alkyl-carbonyl, C₂-C₅-alkenyl-carbonyl, C₁-C₅-alkoxy-carbonyl, C₁-C₅-alkyl, C₁-C₅-alkyl-carbamoyl, aryl-C₁-C₅-alkyl, aryl-carbonyl, aryl-C₁-C₅-alkyl-carbonyl, aryl-C₁-C₅-alkoxy-carbonyl, aryl-carbamoyl, cycloalkyl-carbonyl, cycloalkyl-C₁-C₅-alkyl-carbonyl, cycloalkyl-C₁-C₅-alkoxy-carbonyl, heteroaryl-C₁-C₅-alkyl, heteroaryl-carbonyl, heteroaryl-C₁-C₅-alkyl-carbonyl or heteroaryl-C₁-C₅-alkoxy-carbonyl; with the proviso that when R¹, R², R³ and R⁴ represent hydrogen, R⁵ is not an ethoxy-carbonyl group or a tert.-butoxycarbonyl group.

In a preferred embodiment, the present invention relates to tetrahydropyridoindole derivatives of the general Formula (I), wherein

R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₅-alkoxy or halogen; and R⁵ represents C₀-C₅-alkyl-carbonyl, C₂-C₅-alkenyl-carbonyl, C₁-C₅-alkoxy-carbonyl, C₁-C₅-alkyl-carbamoyl, aryl-C₁-C₅-alkyl, aryl-carbonyl, aryl-C₁-C₅-alkyl-carbonyl, aryl-C₁-C₅-alkoxy-carbonyl, aryl-carbamoyl, aryl-thiocarbamoyl, aryl-C₁-C₅-alkyl-carbamoyl, aryl-C₁-C₅-alkyl-thiocarbamoyl, cycloalkyl-carbonyl, cycloalkyl-C₁-C₅-alkyl-carbonyl, cycloalkyl-carbamoyl or heteroaryl-carbonyl; with the proviso that when R¹, R², R³ and R⁴ represent hydrogen, R⁵ is not an ethoxy-carbonyl group or a tert.-butoxycarbonyl group.

Any reference hereinabove or hereinbelow to a compound of general Formula (I) or (II) is to be understood as referring also to optically pure enantiomers, mixtures of enantiomers, racemates, optically pure diastereoisomers, mixtures of diastereoisomers, diastereoisomeric racemates, mixtures of diastereoisomeric racemates, meso forms and salts [only pharmaceutically acceptable ones in case of a compound of general Formula (II)] of such compounds, as appropriate and expedient.

Preferred tetrahydropyridoindole derivatives of general Formula (I) are those wherein R¹, R², R³ and R⁴ represent hydrogen.

In a preferred embodiment, R¹, R², R³ and R⁴ independently represent C₁-C₅-alkyl, C₁-C₃-alkoxy, halogen, nitro, cyano or formyl, especially C₁-C₅-alkyl, C₁-C₃-alkoxy or halogen.

In another preferred embodiment one or two substituents selected from R¹, R², R³ and R⁴ independently represent methyl, trifluoromethyl, methoxy, fluoro, chloro or bromo.

In a very preferred embodiment R² is selected from C₁-C₅-alkyl, C₁-C₅-alkoxy, halogen and trifluoromethyl, especially from C₁-C₅-alkyl, halogen and trifluoromethyl; R³ is hydrogen or halogen, especially hydrogen; and R¹ and R⁴ are both hydrogen.

In a most especially preferred embodiment R² is selected from methyl, fluoro, chloro, bromo and trifluoromethyl; R³ is hydrogen or chloro, especially hydrogen; and R¹ and R⁴ are both hydrogen.

In a particularly preferred embodiment, R⁵ is selected from the group consisting of 2-cyclohexyl-2-phenyl-acetyl; 2-naphthalen-1-yl-acetyl; 2-naphthalen-2-yl-acetyl; 3-cyclopentyl-propionyl; 3-phenyl-propionyl; acetyl; diphenylacetyl; hexanoyl; (E)-but-2-enoyl; 9H-fluoren-9-ylmethoxycarbonyl; benzyloxycarbonyl; butoxycarbonyl; 3-phenyl-propyl; phenethyl; phenylacetyl; ethylcarbamoyl; 2-bromo-3-methyl-benzoyl; 2-bromo-5-methyl-benzoyl; 2-methoxy-benzoyl; 3,4,5-trimethoxy-benzoyl; 3,5-bis-trifluoromethyl-benzoyl; 3,5-dimethoxy-benzoyl; 3-chloro-benzoyl; 4-bromo-benzoyl; 4-chloro-benzoyl; 4-methoxy-benzoyl; 4-tert.-butyl-benzoyl; 4-trifluoromethoxy-benzoyl; 4-trifluoromethyl-benzoyl; benzoyl; phenylcarbamoyl; 4′-ethyl-biphenyl-4-carbonyl; biphenyl-2-carbonyl; biphenyl-4-carbonyl; 2-methoxy-naphthalene-1-carbonyl; 4-methoxy-naphthalene-1-carbonyl; 2-ethoxy-naphthalene-1-carbonyl; naphthalene-1-carbonyl; cyclohexane-carbonyl; cyclopropane-carbonyl; pyridine-3-carbonyl; 2-chloro-6-methyl-pyridine-4-carbonyl; pyridine-4-carbonyl; furan-2-carbonyl; furan-3-carbonyl; 2-methyl-furan-3-carbonyl; 3-methyl-furan-2-carbonyl; 5-bromo-furan-2-carbonyl; pyrazine-2-carbonyl, benzo[b]thiophene-2-carbonyl; 5-chloro-thiophene-2-carbonyl; 3-methyl-thiophene-2-carbonyl; 5-methyl-thiophene-2-carbonyl; thiophene-2-carbonyl and thiophene-3-carbonyl.

Very preferably R⁵ represents phenyl-carbonyl or naphthyl-carbonyl (especially naphthalene-1-carbonyl), wherein the phenyl or naphthyl moiety is optionally substituted by one or more, especially by one or two, substituents selected from C₁-C₅-alkyl, C₁-C₅-alkoxy and halogen. If R⁵ represents substituted phenyl-carbonyl, the substituents are preferably selected from C₁-C₅-alkyl, such as especially methyl, and halogen, such as especially fluoro, chloro and bromo. If R⁵ represents substituted naphthyl-carbonyl, the substituents are preferably selected from C₁-C₅-alkoxy, such as especially methoxy and ethoxy, and halogen, such as especially fluoro.

A group of preferred compounds are those wherein R¹, R², R³ and R⁴ represent hydrogen, R⁵ represents a C₁-C₅-alkoxy-carbonyl group, an aryl-C₁-C₅-alkyl-carbonyl group, an aryl-carbonyl group or a heteroaryl-carbonyl group, especially an aryl-carbonyl group, very preferably naphthalene-1-carbonyl.

Another group of preferred compounds are those wherein R¹, R², R³ and R⁴ represent hydrogen and R⁵ represents a C₁-C₅-alkoxy-carbonyl group, a phenyl C₁-C₅-alkyl-carbonyl group, a naphthalene-1-carbonyl group or a thiophene-2-carbonyl group.

In a preferred embodiment the present invention relates to tetrahydropyridoindole derivatives of the general Formula (I), wherein

R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₃-alkoxy or halogen; and R⁵ represents C₀-C₅-alkyl-carbonyl; C₁-C₅-alkyl-carbamoyl; C₁-C₅-alkoxy-carbonyl; C₂-C₅-alkenyl-carbonyl; C₃-C₆-cycloalkyl-carbonyl; C₃-C₆-cycloalkyl-C₁-C₃-alkyl-carbonyl; C₃-C₆-cycloalkyl-carbamoyl; C₃-C₆-cycloalkyl-thiocarbamoyl; phenyl-C₁-C₃-alkyl; phenyl-carbonyl or phenyl-C₁-C₃-alkyl-carbonyl wherein the phenyl moiety of these two groups may be mono-, di-, tri- or tetra-substituted by substituents independently selected from C₁-C₄-alkyl, C₁-C₃-alkoxy, halogen, trifluoromethyl and trifluoromethoxy, mono-substituted by C₃-C₆-cycloalkyl, or mono-substituted by a phenyl group which in turn may be substituted by a C₁-C₃-alkyl or C₁-C₃-alkoxy group; phenyl-C₁-C₃-alkoxy-carbonyl; phenyl-carbamoyl or phenyl-thiocarbamoyl wherein these two groups are optionally independently mono- or poly-substituted by C₁-C₅-alkyl and/or halogen; phenyl-C₁-C₃-alkyl-carbamoyl; phenyl-C₁-C₃-alkyl-thiocarbamoyl; biphenyl-carbamoyl; naphthyl-carbonyl, naphthyl-C₁-C₃-alkyl-carbonyl or naphthyl-carbamoyl wherein the naphthyl moieties of these three groups are optionally mono- or poly-substituted by substituents independently selected from C₁-C₃-alkyl, C₁-C₃-alkoxy and halogen; fluorenyl-carbonyl, optionally substituted by oxo; fluorenyl-C₁-C₃-alkoxy-carbonyl; or five- to nine-membered heteroaryl-carbonyl groups containing one to three, preferably 1 or 2, heteroatoms independently selected from oxygen, nitrogen and sulfur wherein said groups may be substituted by one or two groups independently selected from C₁-C₃-alkyl, C₁-C₃-alkoxy, halogen and trifluoromethyl; with the proviso that when R¹, R², R³ and R⁴ represent hydrogen, R⁵ is not an ethoxy-carbonyl group or a tert.-butoxycarbonyl group.

The present invention also relates to tetrahydropyridoindole derivatives of the general Formula (I), wherein

R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₃-alkoxy or halogen; and R⁵ represents C₀-C₅-alkyl-carbonyl; C₁-C₅-alkoxy-carbonyl; C₂-C₅-alkenyl-carbonyl; C₃-C₆-cycloalkyl-carbonyl; C₃-C₆-cycloalkyl-C₁-C₃-alkyl-carbonyl; C₃-C₆-cycloalkyl-C₁-C₃-alkoxy-carbonyl; phenyl-carbonyl or phenyl-C₁-C₃-alkyl-carbonyl wherein the phenyl moiety of said groups may be independently mono-, di- or tri-substituted by C₁-C₄-alkyl, C₁-C₃-alkoxy, halogen, trifluoromethyl or trifluoromethoxy, or mono-substituted by a phenyl group which in turn may be substituted by a C₁-C₃-alkyl or C₁-C₃-alkoxy group; naphthyl-carbonyl; fluorenyl-C₁-C₃-alkoxy-carbonyl; or five- or six-membered heteroaryl-carbonyl groups containing one to three heteroatoms independently selected from oxygen, nitrogen and sulfur wherein said groups may be substituted by one or two groups independently selected from C₁-C₃-alkyl, C₁-C₃-alkoxy, halogen and trifluoromethyl; with the proviso that when R¹, R², R³ and R⁴ represent hydrogen, R⁵ is not an ethoxy-carbonyl group or a tert.-butoxycarbonyl group.

Examples of preferred compounds of general Formula (I) are selected from the group consisting of:

-   (2-benzyloxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-9H-fluoren-9-ylmethoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-acetyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; -   (2-phenylacetyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; -   [2-(3,4,5-trimethoxy-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   (2-cyclohexanecarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   [2-(4-methoxy-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(furan-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   (2-cyclopropanecarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   [2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-methoxy-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-trifluoromethyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3,5-bis-trifluoromethyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3-cyclopentyl-propionyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3-phenyl-propionyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-tert.-butyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-trifluoromethoxy-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-((E)-but-2-enoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3,5-dimethoxy-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   (2-diphenylacetyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-hexanoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; -   [2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-bromo-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(pyridine-3-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   (2-benzoyl-8-methoxy-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-8-bromo-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-6-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   [2-(pyrazine-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-bromo-3-methyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-bromo-5-methyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-chloro-6-methyl-pyridine-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(biphenyl-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(5-bromo-furan-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3-methyl-furan-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-methyl-furan-3-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(benzo[b]thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(5-chloro-thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(furan-3-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-naphthalen-2-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(thiophene-3-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   rac.     [2-(2-cyclohexyl-2-phenyl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   (2-phenylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-ethylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   sodium     (2-phenethyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate; -   sodium     [2-(3-phenyl-propyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetate; -   [2-(2-ethoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3-methyl-thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(5-methyl-thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; and -   [2-(pyridine-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid.

Specifically preferred compounds according to general Formula (I) are:

-   [2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-bromo-3-methyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   (2-benzoyl-8-bromo-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; -   [2-(4-bromo-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; and -   [2-(furan-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid.

In a further very preferred embodiment, the invention relates to a compound of general Formula (I) selected from the group consisting of:

-   5-carboxymethyl-7-chloro-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic     acid tert-butyl ester; -   5-carboxymethyl-8-chloro-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic     acid tert-butyl ester; -   5-carboxymethyl-6-chloro-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic     acid tert-butyl ester; -   5-carboxymethyl-7-methyl-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic     acid tert-butyl ester; -   5-carboxymethyl-8-methyl-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic     acid tert-butyl ester; -   8-bromo-5-carboxymethyl-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic     acid tert-butyl ester; -   5-carboxymethyl-8-fluoro-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic     acid tert-butyl ester; -   [7-chloro-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-chloro-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [6-chloro-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3-chloro-benzoyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3-chloro-benzoyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-bromo-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3-chloro-benzoyl)-8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-chloro-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [6-chloro-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-bromo-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-fluoro-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [7-chloro-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [7-methyl-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-methyl-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-fluoro-2-(2-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-fluoro-2-(4-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-chloro-2-(2-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-chloro-2-(4-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-methoxy-naphthalene-1-carbonyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-methoxy-naphthalene-1-carbonyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-methoxy-naphthalene-1-carbonyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-ethoxy-naphthalene-1-carbonyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-ethoxy-naphthalene-1-carbonyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-methoxy-naphthalene-1-carbonyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-fluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3-fluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3,5-difluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3,4,5-trifluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2,3,4,5-tetrafluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   (2-benzoyl-8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-6-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-8-isopropyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-8-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-7,8-dichloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-8-trifluoromethyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-8-tert-butyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-7-chloro-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-7,8-dimethyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzoyl-7-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   [7-chloro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-chloro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [7-methyl-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-bromo-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4′-ethyl-biphenyl-4-carbonyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-bromo-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4′-ethyl-biphenyl-4-carbonyl)-8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [6-chloro-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [7-chloro-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-chloro-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4′-ethyl-biphenyl-4-carbonyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-methyl-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [6-chloro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-chloro-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [6-chloro-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydropyrido[4,3-b]indol-5-yl]-acetic     acid; -   [7-methyl-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-methyl-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-bromo-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-fluoro-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-fluoro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-bromo-3-methyl-benzoyl)-7-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-bromo-3-methyl-benzoyl)-8-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-bromo-3-methyl-benzoyl)-6-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-bromo-3-methyl-benzoyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-bromo-3-methyl-benzoyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-bromo-2-(2-bromo-3-methyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-bromo-3-methyl-benzoyl)-8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-bromo-2-(2-ethoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-ethoxy-naphthalene-1-carbonyl)-8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [8-chloro-2-(2-ethoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(5-bromo-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-methyl-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-methyl-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(biphenyl-3-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-fluoro-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   2-(9-oxo-9H-fluorene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(9H-fluorene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(9H-fluorene-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2,4,6-trifluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-cyclohexyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(1H-indole-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(2-fluoro-phenylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(3-fluoro-phenylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-fluoro-phenylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   (2-o-tolylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-m-tolylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-p-tolylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-phenethylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   [2-(naphthalen-1-ylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(naphthalen-2-ylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(biphenyl-2-ylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   (2-cyclohexylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   [2-(2-chloro-phenylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   [2-(4-fluoro-phenylthiocarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   (2-phenylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-phenethylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-cyclohexylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-benzylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   [2-(2-chloro-phenylthiocarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic     acid; -   (2-p-tolylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; -   (2-m-tolylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid; and -   (2-o-tolylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic     acid.

A further object of the invention relates to compounds for use as a medicament, wherein said compounds are selected from the group consisting of tetrahydropyridoindole derivatives of the following general Formula (II):

wherein R⁶, R⁷, R⁸ and R⁹ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₅-alkoxy, halogen, nitro, cyano or formyl; R¹⁰ represents C₀-C₅-alkyl-carbonyl, C₂-C₅-alkenyl-carbonyl, C₁-C₅-alkoxy-carbonyl, C₁-C₅-alkyl, C₁-C₅-alkyl-carbamoyl, aryl-C₁-C₅-alkyl, aryl-carbonyl, aryl-C₁-C₅-alkyl-carbonyl, aryl-C₁-C₅-alkoxy-carbonyl, aryl-carbamoyl, aryl-thiocarbamoyl, aryl-C₁-C₅-alkyl-carbamoyl, aryl-C₁-C₅-alkyl-thiocarbamoyl, cycloalkyl-carbonyl, cycloalkyl-C₁-C₅-alkyl-carbonyl, cycloalkyl-C₁-C₅-alkoxy-carbonyl, cycloalkyl-carbamoyl, heteroaryl-C₁-C₅-alkyl, heteroaryl-carbonyl, heteroaryl-C₁-C₅-alkyl-carbonyl or heteroaryl-C₁-C₅-alkoxy-carbonyl; and optically pure enantiomers, mixtures of enantiomers, racemates, optically pure diastereoisomers, mixtures of diastereoisomers, diastereoisomeric racemates, mixtures of diastereoisomeric racemates, meso forms and pharmaceutically acceptable salts thereof.

The present invention also relates to compounds of general Formula (II) for use as a medicament, wherein

R⁶, R⁷, R⁸ and R⁹ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₅-alkoxy, halogen, nitro, cyano or formyl; and R¹⁰ represents C₀-C₅-alkyl-carbonyl, C₂-C₅-alkenyl-carbonyl, C₁-C₅-alkoxy-carbonyl, C₁-C₅-alkyl, C₁-C₅-alkyl-carbamoyl, aryl-C₁-C₅-alkyl, aryl-carbonyl, aryl-C₁-C₅-alkyl-carbonyl, aryl-C₁-C₅-alkoxy-carbonyl, aryl-carbamoyl, cycloalkyl-carbonyl, cycloalkyl-C₁-C₅-alkyl-carbonyl, cycloalkyl-C₁-C₅-alkoxy-carbonyl, heteroaryl-C₁-C₅-alkyl, heteroaryl-carbonyl, heteroaryl-C₁-C₅-alkyl-carbonyl or heteroaryl-C₁-C₅-alkoxy-carbonyl.

The present invention also relates to pharmaceutical compositions comprising at least one tetrahydropyridoindole derivative of the general Formula (II), or pharmaceutically acceptable salts thereof, and inert carrier materials and/or adjuvants.

The preferred embodiments described for the compounds of general Formula (I) are also preferred with regard to the pharmaceutical use of the compounds of the present invention such as their use as a medicament and their use in pharmaceutical compositions, especially for the treatment of the diseases mentioned herein.

Pharmaceutical compositions comprising at least one tetrahydropyridoindole derivative of the general Formula (II) are particularly useful for the prevention or treatment of diseases selected from the group consisting of both chronic and acute allergic/immune disorders such as allergic asthma, rhinitis, chronic obstructive pulmonary disease (COPD), dermatitis, inflammatory bowel disease, rheumatoid arthritis, allergic nephritis, conjunctivitis, atopic dermatitis, bronchial asthma, food allergy, systemic mast cell disorders, anaphylactic shock, urticaria, eczema, itching, inflammation, ischemia-reperfusion injury, cerebrovascular disorders, pleuritis, ulcerative colitis, eosinophil-related diseases, such as Churg-Strauss syndrome and sinusitis, and basophil-related diseases, such as basophilic leukemia and basophilic leukocytosis

Another object of the present invention is a method for the treatment or prophylaxis of disease states mediated by CRTH2 comprising the administration to the patient of a pharmaceutically active amount of a tetrahydropyridoindole derivative according to general Formula (II).

In a preferred embodiment of the invention, said amount is comprised between 1 mg and 1000 mg per day, particularly from 2 mg to 500 mg per day, more particularly from 5 mg to 200 mg per day.

Furthermore, the present invention also concerns a process for the preparation of a pharmaceutical composition comprising at least one tetrahydropyridoindole derivative according to general Formula (II) by mixing one or more active ingredients according to general Formula (II) with inert carrier materials and/or adjuvants in a manner known per se.

The present invention also relates to the use of a tetrahydropyridoindole derivative according to general Formula (II) in the preparation of a medicament for the prevention or treatment of the diseases mentioned herein.

These pharmaceutical compositions can be administered enterally, such as orally (e.g. in the form of tablets, coated tablets, dragées, hard and soft gelatine capsules, solutions, emulsions or suspensions), nasally (e.g. in the form of nasal sprays), rectally (e.g. in the form of suppositories) or dermally. However, the administration can also be effected parenterally, such as intramuscularly or intravenously (e.g. in the form of injection solutions).

Pharmaceutical compositions comprising at least one compound of the general Formula (II) can be processed with pharmaceutically inert, inorganic or organic carrier materials and/or adjuvants for the production of tablets, coated tablets, dragées, and hard gelatine capsules. Lactose, corn starch or derivatives thereof, talc, stearic acid or its salts etc. can be used, for example, as such carrier materials or adjuvants for tablets, dragées, and hard gelatine capsules. Suitable carrier materials or adjuvants for soft gelatine capsules, are, for example, vegetable oils, waxes, fats, semi-solid substances and liquid polyols etc.

Suitable carrier materials or adjuvants for the production of solutions and syrups are, for example, water, polyols, saccharose, invert sugar, glucose etc. Suitable carrier materials or adjuvants for injection solutions are, for example, water, alcohols, polyols, glycerol, vegetable oils, etc. Suitable carrier materials or adjuvants for suppositories are, for example, natural or hardened oils, waxes, fats, semi-solid or liquid polyols, etc.

The above-described components for orally administered or injectable compositions are merely representative. Further materials as well as processing techniques and the like are set out in Remington's Pharmaceutical Sciences, 20^(th) Edition, 2001, Marek Publishing Company, Easton, Pa., which is incorporated herein by reference.

These pharmaceutical compositions according to the invention can also be administered in sustained release forms or by using sustained release drug delivery systems.

A further object of the invention is a process for preparing tetrahydropyridoindole derivatives according to general Formula (I). Compounds according to general Formula (I) of the present invention are prepared according to the general sequence of reactions outlined in the schemes below, wherein R¹, R², R³, R⁴ and R⁵ are as defined in general Formula (I). The compounds obtained may also be converted into a pharmaceutically acceptable salt thereof in a manner known per se.

Compounds of the invention may be manufactured by the application or adaptation of known methods, by which is meant methods used hereinafter or described in the literature, for example those described by Larock R. C. in “Comprehensive organic transformations: a guide to functional group preparations”, VCH publishers, (1999).

In the reactions described hereinafter, it may be necessary to protect reactive functional groups, for example hydroxy, amino, imino, thio or carboxy groups, where these are desired in the final product, to avoid their unwanted participation in the reactions. Conventional protecting groups may be used in accordance with standard practice, for example see Greene T. W. and Wuts P. G. M. in “Protective groups in organic synthesis” Wiley-Interscience (1999).

Generally, tetrahydropyridoindole derivatives of general Formula (I) are prepared as shown in Schemes 1 and 2, by condensing phenylhydrazine of Formula 1 and 4-piperidone monohydrate hydrochloride of Formula 2 in a Fischer indole synthesis to produce tetrahydropyridoindole of Formula 3, using conditions known to a skilled person (e.g. M. H. Block et al., J. Med. Chem. (2002), 45, 3509-3523). The nitrogen atom in Formula 3 is protected with a protecting group (PG), such as alkoxycarbonyl, preferably tert.-butoxycarbonyl, or benzyloxycarbonyl, under standard conditions, affording a compound of Formula 4. Then, compound of Formula 4 reacts with a compound of Formula L-CH₂CO₂R in which R is an alkyl group, preferably ethyl or tert.-butyl and L is a leaving group, in the presence of a base, such as caesium carbonate, sodium hydride, potassium tert.-butanolate or the like, in a suitable solvent, such as acetone, tetrahydrofuran or dioxane, to generate a compound of Formula 5. Suitable L is a leaving group such as halo, in particular bromo or chloro; mesyloxy or tosyloxy. Preferably, the compound of Formula L-CH₂CO₂R is ethyl bromo-acetate. Deprotection under standard conditions delivers an intermediate of Formula 6.

As illustrated in Scheme 2, intermediate of Formula 6 reacts in Step a) with a reagent of Formula L-R⁵, where R⁵ is as defined in general Formula (I) hereinabove and L is a leaving group, such as hydroxy, or halo, in particular chloro or bromo. R⁵ transferring reagent of Formula L-R⁵ may be a chloroformate (Method A); or an acyl halide, preferably an acid chloride, or bromide, used as such (Method B); or generated in situ from the corresponding acid with a halogenating reagent under conditions known to a skilled person, preferably by means of oxalyl chloride or phosphorous oxychloride (Method C); or an acyl anhydride, transferring R⁵ in the presence of a base, such as triethylamine, N,N-diisopropylethylamine, N-ethyl-morpholine, N-methylpiperidine, or pyridine, in a suitable solvent, such as dichloro-methane, tetrahydrofurane, or N,N-dimethylformamide, to give a product of Formula 7.

In another aspect, a carboxylic acid is used in the presence of a coupling reagent (Method D), such as 1,3-dicyclohexylcarbodiimide, diisopropylcarbodiimid, O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate and the like, in the presence of a base described hereinabove, to give an amide of Formula 7.

In a further aspect, isocyanates or isothiocyanates (Method E), or alkylhalides (Method F) are used in the presence of a base to form products of Formula 7.

Hydrolysis of the ester group R in Formula 7 can be carried out using routine procedures, as outlined in Scheme 2, Step b), for example by stirring with aqueous sodium hydroxide, or trifluoroacetic acid to give a compound of general Formula (I).

Alternatively, tetrahydropyridoindoles of general Formula (I) can be synthesized in three consecutive steps as outlined in Scheme 3, starting from abovementioned Fischer indole product of Formula 3, which is reacted first in a substitution reaction with abovementioned reagent of Formula L-R⁵, using conditions as described in Methods A to F, to give a compound of Formula 8. Subsequent alkylation of the indole nitrogen can be performed with a compound of the abovementioned Formula L-CH₂CO₂R, in which R and L is as defined above, under conditions as described in Scheme 1 for the alkylation of compound of Formula 4, to give a precursor of Formula 7. Final deprotection under standard conditions, as outlined in Scheme 2, Step b) delivers a compound of general Formula (I).

In the following the present invention shall be illustrated by means of examples, which are not construed to be viewed as limiting the scope of the invention.

Experimental Section: Abbreviations:

-   AcOH acetic acid

BSA Bovine Serum Albumine

calcd calculated CH₂Cl₂ dichloromethane

DIEA N,N-diisopropylethylamine DMF Dimethylformamide DMSO Dimethylsulfoxide

EDTA ethylenediamine tetraacetic acid

Et₃N Triethylamine ETOAc Ethyl Acetate EtOH Ethanol

Ex. Example(s)

FLIPR Fluorescent Imaging Plate Reader

g gram h hour H₂O water HCl hydrochloric acid

HBSS Hank's Balanced Salt Solution

HEPES 4-(2-Hydroxyethyl)-piperazine-1-ethanesulfonic acid

HPLC High Performance Liquid Chromatography

k kilo K₂CO₃ potassium carbonate KHSO₄ potassium hydrogen sulfate l liter

LC Liquid Chromatography

LDA Lithium di-isopropyl amide

MeOH Methanol

MgCl₂ magnesium chloride MgSO₄ magnesium sulfate μ micro m milli M molar Me methyl MeOH methanol min minutes mol mole

ESI-MS Electrospray Ionization Mass Spectroscopy

N Normality of solution NaHCO₃ sodium hydrogenocarbonate NaN₃ sodium azide Na₂CO₃ sodium carbonate NaCl sodium chloride NaOH sodium hydroxide Na₂SO₄ sodium sulfate NH₄OH ammonium acetate PyBOP Benzotriazole-1-yl-oxy-tris-pyrrolidino-phosphonium-hexafluorophosphate PBS phosphate buffer saline

PGD₂ Prostaglandin D2

PMSF phenyl methylsulfonyl fluoride POCl₃ phosphorous oxychloride t_(R) retention time sat. saturated

THF Tetrahydrofuran

Tris tris-(hydroxymethyl)aminomethane buffer

Chemistry General Remarks:

Temperatures are indicated in degrees Celsius (° C.). Unless otherwise indicated, the reactions take place at room temperature (rt).

In mixtures, relations of parts of solvent or eluent or reagent mixtures in liquid form are given as volume relations (v/v), unless indicated otherwise.

Analytical HPLC conditions as used in the Examples below:

-   -   LC-1: Analytical HPLC on a Xterra™ MS C₁₈ column (50×2.1 mm, 5         μm, Waters): Linear gradient of water/0.06% formic acid (LC-1)         and acetonitrile/0.06% formic acid (B) from 5% to 95% B over 6         min; flow rate 0.25 ml/min, detection at 215 nm.     -   LC-2: Analytical HPLC on a GromSil MS C₁₈ column (50×2.1 mm, 5         μm, Waters): Linear gradient of water/0.06% formic acid (LC-1)         and acetonitrile/0.06% formic acid (B) from 5% to 95% B over 6         min; flow rate 0.25 ml/min, detection at 215 nm.     -   LC-3: Analytical HPLC on a Waters Xterra™ MS C18 column (4.6×50         mm, 5 mm): Linear gradient of water/0.06% formic acid (A) and         acetonitrile/0.06% formic acid (B) from 5% to 95% B over 1 min;         flow rate 3 ml/min.     -   LC-4: Analytical HPLC on a Zorbax SB-AQ column (4.6×50 mm, 5         mm): Linear gradient of water/0.06% formic acid (A) and         acetonitrile/0.06% formic acid (B) from 5% to 95% B over 1 min;         flow rate 3 ml/min.     -   LC-5: Analytical HPLC on a Zorbax SB-AQ column (50×4.6 mm, 5 mm,         Agilent 1100 equipped with a binary pump Dionex P580, a         Photodiode Array Detector Dionex PDA-100 and a mass spectrometer         Finnigan AQA): Linear gradient of water/0.04% TFA (A) and         acetonitrile (B) from 5% to 95% B over 1 min; flow rate 4.5         ml/min, detection at 210, 220, 230, 254 and 280 nm.     -   LC-6: Analytical HPLC on a Waters Xterra™ MS C18 column (2.1×50         mm, 5 mm): Linear gradient of water/0.06% formic acid (A) and         acetonitrile/0.06% formic acid (B) from 5% to 95% B over 2 min;         flow rate 0.75 ml/min.

Preparation of 1,2,3,4-tetrahydro-pyrido[4,3-b]indole (Intermediates of Formula 6) Intermediate 1: Ethyl (1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

A solution of ethyl (2-tert.-butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate (8.45 g, 23.6 mmol) in ethyl acetate (80 ml) is treated with a solution of 3M HCl in ethyl acetate (39.3 ml). After stirring at room temperature for 3 h, the solvent is removed in vacuo and the residue azeotroped twice with toluene. The crude product is suspended in diethyl ether, filtered off, washed with diethyl ether and dried. Finally, pure title compound is obtained as beige solid (5.49 g) in 79% yield. t_(R) (LC-2) 1.41 min; ESI-MS (positive ion): m/z 259.33 [M+H]⁺ (calcd 258.32 for C₁₅H₁₈N₂O₇).

1a) 2,3,4,5-Tetrahydro-1H-pyrido[4,3-b]indole hydrochloride

4-Piperidone monohydrate hydrochloride (10 g, 65.1 mmol) and phenylhydrazine hydrochloride (9.4 g, 65.1 mmol) are suspended in ethanol (200 ml) and stirred at reflux overnight. The resulting solid is filtered off and washed with diethyl ether to afford pure sub-title compound (11.9 g) in 88% yield. t_(R) (LC-2) 0.89; ESI-MS (positive ion): m/z 173.34 [M+H]⁺ (calcd 172.23 for C₁₁H₁₂N₂).

1b) 2-tert.-Butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indole

A solution of di-tert.-butyl-dicarbonate (7.3 ml, 35.2 mmol) in dry dichloromethane (100 ml) is added to a mixture of 2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole hydrochloride (7.0 g, 33.5 mmol) and DIEA (20 ml, 117 mmol) in dry dichloromethane (200 ml). After stirring at rt for 2 h, water (100 ml) and 2N aqueous KHSO₄ solution (60 ml) are added. The organic layer is separated and washed successively with water and brine, dried over Mg₂SO₄, filtered and evaporated, affording crude sub-title compound as yellow oil, which solidified upon standing and is used in the next step without further purification. t_(R) (LC-2) 2.31 min; ESI-MS (positive ion): m/z 295.37 [M+Na]⁺ (calcd 272.34 for C₁₆H₂₀N₂O₂).

1c) Ethyl (2-tert.-butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate

To a stirred suspension of crude 2-tert.-butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol (33.5 mmol) and caesium carbonate (25.1 g, 77.1 mmol) in dry acetone is added ethyl bromoacetate (5.6 ml, 50.3 mmol). The reaction mixture is stirred at rt overnight and then filtered over a small plug of Celite. The filtrate is concentrated under reduced pressure and the residue is purified by silica gel column chromatography (hexane/EtOAc 5:1) to afford pure sub-title compound as yellow oil (8.45 g) in 70% yield (over two steps). t_(R) (LC-2) 2.46 min; ESI-MS (positive ion): m/z 381.54 [M+Na]⁺ (calcd 358.43 for C₂₀H₂₆N₂O₄).

Intermediate 2: Ethyl (8-bromo-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 4-bromophenylhydrazine for phenylhydrazine in Step 1a).

Intermediate 3: Ethyl (8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 4-methylphenylhydrazine for phenylhydrazine in Step 1a).

Intermediate 4: Ethyl (7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 3-methylphenylhydrazine for phenylhydrazine in Step 1a).

Intermediate 5: Ethyl (7-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 3-chlorophenylhydrazine for phenylhydrazine in Step 1a).

Intermediate 6: Ethyl (8-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 4-chlorophenylhydrazine for phenylhydrazine in Step 1a).

Intermediate 7: Ethyl (6-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 2-chlorophenylhydrazine for phenylhydrazine in Step 1a).

Intermediate 8: Ethyl (8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 4-fluorophenylhydrazine for phenylhydrazine in Step 1a).

Intermediate 9: Ethyl (6-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 2-methylphenylhydrazine for phenylhydrazine in Step 1a).

Intermediate 10: Ethyl (7-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 3-fluorophenylhydrazine for phenylhydrazine in Step 1a).

Intermediate 11: Ethyl (7,8-dichloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 3,4-dichlorophenylhydrazine for phenylhydrazine in Step 1a).

Intermediate 12: Ethyl (8-trifluoromethyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 4-trifluoromethylhydrazine for phenylhydrazine in Step 1a).

Intermediate 13: Ethyl (8-tert-butyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate to hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 4-tert-butylhydrazine for phenylhydrazine in Step 1a).

Intermediate 14: Ethyl (7-Chloro-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 3-chloro-4-methylhydrazine for phenylhydrazine in Step 1a).

Intermediate 15: Ethyl (7,8-dimethyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 3,4-dimethylhydrazine for phenylhydrazine in Step 1a).

Intermediate 16: Ethyl (8-isopropyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 4-isopropylhydrazine for phenylhydrazine in Step 1a).

Intermediate 17: Ethyl (3-methoxy-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride

The title compound is prepared using a procedure analogous to Intermediate 1, substituting 3-chloro-4-methylhydrazine for phenylhydrazine in Step 1a).

Example 1 (2-tert.-Butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid

A stirred solution of ethyl (2-tert.-butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate (15 mg, 0.039 mmol) in THF (0.6 ml) is treated with 0.2 N aqueous NaOH (0.29 ml, 0.058 mmol) at rt for 15 min. The reaction mixture is diluted with water (2 ml) and washed with diethyl ether (2 ml), then neutralized with conc. HCl (58 μl), and extracted with dichloromethane. The solvent is evaporated and the crude product is recrystallized from acetonitrile to afford pure compound as a yellow solid: t_(R) (LC-1) 2.16 min; ESI-MS (positive ion): m/z 353.32 [M+Na]⁺ (calcd 330.38 for C₁₈H₂₂N₂O₄).

Example 2 (2-Benzyloxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid (Method A)

To a stirred solution of Intermediate 1 (29.5 mg, 0.10 mmol) and DIEA (51 μl, 0.30 mmol) in dichloromethane (1 ml) is added benzyl chloroformate (16 μl, 0.11 mmol). The reaction mixture is stirred at it for 1 h, 1N aqueous HCl (2 ml). The aqueous layer is extracted twice with dichloromethane. The combined organic layers are washed with water, saturated NaHCO₃ solution, then are concentrated to dryness to afford crude ethyl (2-benzyloxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate: t_(R) (LC-1) 2.52 min; ESI-MS (positive ion): m/z 393.19 [M]⁺ (calcd 392.45 for C₂₃H₂₄N₂O₄).

The title compound is obtained using conditions for the hydrolysis of the above crude analogous to Example 1: t_(R) (LC-1) 2.22 min; ESI-MS (positive ion): m/z 387.14 [M+Na]⁺ (calcd 364.40 for C₂₁H₂₀N₂O₄).

Examples 3-5 of the following Table 1 are prepared using a procedure analogous to that described for Example 2, substituting the appropriate chloroformates for benzyl chloroformate.

TABLE 1 Mol Formula t_(R) [min] MS Data Ex. Name Mol Weight (Methode) m/z [M + H]⁺ 3 (2-butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3- C18H22N2O4 2.22 331.22 b]indol-5-yl)-acetic acid 330.38 (LC-1) 4 (2-ethoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3- C16H18N2O4 1.95 303.33 b]indol-5-yl)-acetic acid 302.33 (LC-1) 5 (2-9H-fluoren-9-ylmethoxycarbonyl-1,2,3,4- C28H24N2O4 2.46 453.21 tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid 452.51 (LC-1)

Example 6 [2-(Naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid (Method B)

Step a): To a stirred solution of Intermediate 1 (ethyl (1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate hydrochloride, 25.0 mg, 0.085 mmol) and DIEA (73 μl, 0.425 mmol) in dichloromethane (0.5 ml) is added naphthoyl chloride (15 mg, 0.11 mmol). The resulting yellow solution was kept stirring at rt for 1 h and then is quenched by adding saturated aqueous NaHCO₃ solution (2 ml). The organic layer is separated and washed with water (2 ml). After removal of the solvent, crude ethyl (2-benzoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate is obtained pure as a yellow glassy solid: t_(R) (LC-2) 2.20 min; ESI-MS (positive ion): m/z 386.31 [M+Na]⁺ (calcd 362.42 for C₂₂H₂₂N2O₃).

Step b): A solution of crude ethyl (2-benzoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate (0.085 mmol) in THF (0.5 ml) is treated with 0.2 N aqueous NaOH solution (0.64 ml) at rt for 15 min. Then, the yellow reaction mixture is diluted with water (2 ml), washed with diethyl ether (2 ml), acidified with cone. HCl to pH 1 and extracted with dichloromethane. The combined organic phases are washed with water, then dried over Na₂SO₄, filtered and the solvent evaporated. The crude product is recrystallized from diisopropyl ether to give pure title compound as yellow solid: t_(R) (LC-1) 2.95 min; ESI-MS (positive ion): m/z 335.17 [M+H]⁺ (calcd 334.37 for C₂₀H₁₈N₂O₃).

Examples 7-31 of the following Table 2 are prepared using a procedure analogous to that described for Example 6, substituting the appropriate acid chloride for naphthoylchloride.

TABLE 2 Mol Formula t_(R) [min] MS Data Ex. Name Mol Weight (Methode) m/z [M + H]⁺ 7 (2-acetyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5- C15H16N2O3 1.65 273.21 yl)-acetic acid 272.30 (LC-2) 8 (2-phenylacetyl-1,2,3,4-tetrahydro-pyrido[4,3- C21H20N2O3 1.97 349.37 b]indol-5-yl)-acetic acid 348.40 (LC-1) 9 (2-benzoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol- C20H18N2O3 1.95 335.17 5-yl)-acetic acid 334.37 (LC-1) 10 [2-(3,4,5-trimethoxy-benzoyl)-1,2,3,4-tetrahydro- C23H24N2O6 1.92 425.17 pyrido[4,3-b]indol-5-yl]-acetic acid 424.45 (LC-1) 11 (2-cyclohexanecarbonyl-1,2,3,4-tetrahydro- C20H24N2O3 2.08 341.22 pyrido[4,3-b]indol-5-yl)-acetic acid 340.42 (LC-1) 12 [2-(4-methoxy-benzoyl)-1,2,3,4-tetrahydro- C21H20N2O4 1.96 365.17 pyrido[4,3-b]indol-5-yl]-acetic acid 364.40 (LC-1) 13 [2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro- C18H16N2O3S 1.94 341.09 pyrido[4,3-b]indol-5-yl]-acetic acid 340.40 (LC-1) 14 [2-(furan-2-carbonyl)-1,2,3,4-tetrahydro- C18H16N2O4 1.86 325.11 pyrido[4,3-b]indol-5-yl]-acetic acid 324.34 (LC-1) 15 (2-cyclopropanecarbonyl-1,2,3,4-tetrahydro- C17H18N2O3 1.82 299.12 pyrido[4,3-b]indol-5-yl)-acetic acid 298.34 (LC-1) 16 [2-(2-methoxy-benzoyl)-1,2,3,4-tetrahydro- C21H20N2O4 1.94 365.17 pyrido[4,3-b]indol-5-yl]-acetic acid 364.40 (LC-1) 17 [2-(4-trifluoromethyl-benzoyl)-1,2,3,4-tetrahydro- C21H17N2O3F3 2.16 403.13 pyrido[4,3-b]indol-5-yl]-acetic acid 402.37 (LC-1) 18 [2-(3,5-bis-trifluoromethyl-benzoyl)-1,2,3,4- C22H16N2O3F6 2.34 471.11 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 470.37 (LC-1) 19 [2-(3-cyclopentyl-propionyl)-1,2,3,4-tetrahydro- C21H26N2O3 2.22 355.17 pyrido[4,3-b]indol-5-yl]-acetic acid 354.45 (LC-1) 20 [2-(3-phenyl-propionyl)-1,2,3,4-tetrahydro- C22H22N2O3 2.09 363.19 pyrido[4,3-b]indol-5-yl]-acetic acid 362.43 (LC-1) 21 [2-(biphenyl-4-carbonyl)-1,2,3,4-tetrahydro- C26H22N2O3 2.26 411.16 pyrido[4,3-b]indol-5-yl]-acetic acid 410.47 (LC-1) 22 [2-(4-tert-butyl-benzoyl)-1,2,3,4-tetrahydro- C24H26N2O3 2.29 391.22 pyrido[4,3-b]indol-5-yl]-acetic acid 390.48 (LC-1) 23 [2-(4-trifluoromethoxy-benzoyl)-1,2,3,4- C21H17N2O4F3 2.20 419.06 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 418.37 (LC-1) 24 [2-((E)-but-2-enoyl)-1,2,3,4-tetrahydro- C17H18N2O3 1.82 299.12 pyrido[4,3-b]indol-5-yl]-acetic acid 298.34 (LC-1) 25 [2-(4-chloro-benzoyl)-1,2,3,4-tetrahydro- C20H17N2O3Cl 2.10 369.12 pyrido[4,3-b]indol-5-yl]-acetic acid 368.82 (LC-1) 26 [2-(3,5-dimethoxy-benzoyl)-1,2,3,4-tetrahydro- C22H22N2O5 2.01 395.17 pyrido[4,3-b]indol-5-yl]-acetic acid 394.43 (LC-1) 27 (2-diphenylacetyl-1,2,3,4-tetrahydro-pyrido[4,3- C27H24N2O3 2.27 425.17 b]indol-5-yl)-acetic acid 424.50 (LC-1) 28 (2-hexanoyl-1,2,3,4-tetrahydro-pyrido[4,3- C19H24N2O3 2.10 329.25 b]indol-5-yl)-acetic acid 328.41 (LC-1) 29 [2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro- C20H17N2O3Cl 2.08 369.12 pyrido[4,3-b]indol-5-yl]-acetic acid 368.82 (LC-1) 30 [2-(4-bromo-benzoyl)-1,2,3,4-tetrahydro- C20H17N2O3Br 2.11 415.05 pyrido[4,3-b]indol-5-yl]-acetic acid 413.27 (LC-1) 31 [2-(pyridine-3-carbonyl)-1,2,3,4-tetrahydro- C19H17N3O3 1.62 336.25 pyrido[4,3-b]indol-5-yl]-acetic acid 335.36 (LC-1)

Example 32 (2-Benzoyl-8-methoxy-1,2,3,4-tetrahydro-pyrido[4,3-b]-5-yl)-acetic acid

The title compound is obtained using conditions for the hydrolysis of ethyl (8-methoxy-2-phenylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate analogous to Example 1: t_(R) (LC-1) 1.92; ESI-MS (positive ion): m/z 364.23 [M]⁺ (calcd 364.39 for C₂₁H₂₀N₂O₄).

32a) 8-Methoxy-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole

A suspension of 4-piperidone monohydrate hydrochloride (1.0 g, 6.5 mmol) and 4-methoxyphenylhydrazine hydrochloride (1.14 g, 6.5 mmol) in ethanol (17 ml) is kept stirring at reflux overnight. The resulting solid is filtered off and washed with diethyl ether to afford crude sub-title compound, which is used without further purification: t_(R) (LC-1) 0.38; ESI-MS (positive ion): m/z 203.19 [M+H]⁺ (calcd 202.25 for C₁₂H₁₄N₂O).

32b) 8-Methoxy-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic acid phenylamide

The subtitle compound is prepared using Method B as described for Example 6, substituting 8-methoxy-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole for Intermediate 1: t_(R) (LC-1) 2.03; ESI-MS (positive ion): m/z 307.21 [M+H]⁺ (calcd 306.36 for C₁₉H₁₈N₂O₂).

32c) Ethyl (8-methoxy-2-phenylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate

The subtitle compound is prepared according to Step 1c) in the procedure described for the synthesis of Intermediate 1, substituting 8-methoxy-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic acid phenylamide for 2-tert.-butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indole: t_(R) (LC-1) 2.21 min; ESI-MS (positive ion): m/z 393.32 [M+H]⁺ (calcd 392.17 for C₂₃H₂₄N₂O₄).

Examples 33-36 of the following Table 3 are prepared using a procedure analogous to that described for Example 32, substituting the appropriate phenylhydrazine for 4-methoxyphenylhydrazine.

TABLE 3 Mol Formula t_(R) [min] MS Data Ex. Name Mol Weight (Methode) m/z [M + H]⁺ 33 (2-benzoyl-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3- C21H20N2O3 2.03 349.24 b]indol-5-yl)-acetic acid 348.40 (LC-1) 34 (2-benzoyl-8-bromo-1,2,3,4-tetrahydro-pyrido[4,3- C20H17BrN2O3 2.11 413.13 b]indol-5-yl)-acetic acid 413.26 (LC-1) 35 (2-benzoyl-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3- C21H20N2O3 2.05 349.18 b]indol-5-yl)-acetic acid 348.40 (LC-1) 36 (2-benzoyl-6-methyl-1,2,3,4-tetrahydro-pyrido[4,3- C21H20N2O3 2.01 349.24 b]indol-5-yl)-acetic acid 348.40 (LC-1)

Example 37 [2-(2-Cyclohexyl-2-phenyl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid (Method C)

Step a): To a stirred solution of Intermediate 1 (25 mg, 0.085 mmol), cyclohexyl-phenylacetic acid (27.7 mg, 0.127 mmol) and DIEA (73 μl, 0.424 mmol) in dichloromethane (1 ml) is added POCl₃ (9 μl, 0.093 mmol). The resulting yellow reaction mixture is stirred at rt overnight, then saturated aqueous NaHCO₃ solution (2 ml) is added. The organic layer is separated and washed with water (2 ml). Evaporation of the solvent gave a crude that is purified by silica gel column chromatography (hexane/EtOAc 3:1) affording ethyl [2-(2-cyclohexyl-2-phenyl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetate as a white solid (29 mg) in 74% yield: t_(R) (LC-2) 2.74 min; ESI-MS (positive ion): m/z 459.25 [M+H]⁺ (calcd 458.59 for C₂₉H₃₄N₂O₃).

Step b): The title compound is obtained using conditions for the hydrolysis of the above ester analogous to Example 1: t_(R) (LC-2) 2.47 min; ESI-MS (positive ion): m/z 431.22 [M+H]⁺ (calcd 430.55 for C₂₇H₃₀N₂O₃).

Examples 38-52 of the following Table 4 are prepared using a procedure analogous to that described for Example 37, substituting the appropriate acid for cyclohexylphenylacetic acid.

TABLE 4 Mol Formula t_(R) [min] MS Data Ex. Name Mol Weight (Methode) m/z [M + H]⁺ 38 [2-(pyrazine-2-carbonyl)-1,2,3,4-tetrahydro- C18H16N4O3 1.80 337.14 pyrido[4,3-b]indol-5-yl]-acetic acid 336.35 (LC-1) 39 [2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro- C28H26N2O3 2.50 439.18 pyrido[4,3-b]indol-5-yl]-acetic acid 438.53 (LC-1) 40 [2-(2-bromo-3-methyl-benzoyl)-1,2,3,4-tetrahydro- C21H19N2O3Br 2.15 429.05 pyrido[4,3-b]indol-5-yl]-acetic acid 427.30 (LC-1) 41 [2-(2-bromo-5-methyl-benzoyl)-1,2,3,4-tetrahydro- C21H19N2O3Br 2.17 429.05 pyrido[4,3-b]indol-5-yl]-acetic acid 427.30 (LC-1) 42 [2-(2-chloro-6-methyl-pyridine-4-carbonyl)-1,2,3,4- C20H18N3O3Cl 2.00 384.08 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 383.83 (LC-1) 43 [2-(biphenyl-2-carbonyl)-1,2,3,4-tetrahydro- C26H22N2O3 2.23 411.15 pyrido[4,3-b]indol-5-yl]-acetic acid 410.47 (LC-1) 44 [2-(5-bromo-furan-2-carbonyl)-1,2,3,4-tetrahydro- C18H15N2O4Br 2.10 403.00 pyrido[4,3-b]indol-5-yl]-acetic acid 403.23 (LC-1) 45 [2-(3-methyl-furan-2-carbonyl)-1,2,3,4-tetrahydro- C19H18N2O4 2.01 339.12 pyrido[4,3-b]indol-5-yl]-acetic acid 338.36 (LC-1) 46 [2-(2-methyl-furan-3-carbonyl)-1,2,3,4-tetrahydro- C19H18N2O4 1.97 339.18 pyrido[4,3-b]indol-5-yl]-acetic acid 338.36 (LC-1) 47 [2-(benzo[b]thiophene-2-carbonyl)-1,2,3,4- C22H18N2O3S 2.23 391.09 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 390.46 (LC-1) 48 [2-(5-chloro-thiophene-2-carbonyl)-1,2,3,4- C18H15N2O3ClS 2.20 375.04 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 374.85 (LC-1) 49 [2-(furan-3-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3- C18H16N2O4 1.89 325.17 b]indol-5-yl]-acetic acid 324.34 (LC-1) 50 [2-(2-naphthalen-2-yl-acetyl)-1,2,3,4-tetrahydro- C25H22N2O3 2.23 399.18 pyrido[4,3-b]indol-5-yl]-acetic acid 398.46 (LC-1) 51 [2-(thiophene-3-carbonyl)-1,2,3,4-tetrahydro- C18H16N2O3S 1.96 341.09 pyrido[4,3-b]indol-5-yl]-acetic acid 340.40 (LC-1) 52 [2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro- C25H22N2O3 2.24 399.18 pyrido[4,3-b]indol-5-yl]-acetic acid 398.46 (LC-1)

Example 53 [2-(2-Ethoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid (Method D)

Step a): To a solution of 2-ethoxynaphthoic acid (22 mg, 0.1 mmol), N′,N′,N′,N′-tetramethyl-O-(7-azabenzotriazole-1-yl)-uronium-hexafluorophosphate (38 mg, 0.1 mmol) and DIEA (51 μl, 0.3 mmol) in THF/DMF (4:1, 1 ml) is added Intermediate 1 (29 mg, 0.1 mmol) in one portion and the reaction mixture is stirred at rt overnight. Then, the solvent is evaporated and the residue purified by silica gel column chromatography (6% MeOH in CH₂Cl₂/aqueous NH₄OH 9:1) affording ethyl [2-(2-ethoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetate (43 mg) as a glassy brown solid in 93% yield.

Step b): The title compound is obtained using conditions for the hydrolysis of the above ester analogous to Example 1: t_(R) (LC-2) 2.49 min; ESI-MS (positive ion): m/z 429.24 [M+H]⁺ (calcd 428.48 for C₂₆H₂₄N₂O₄).

Examples 54-56 of the following Table 5 are prepared using a procedure analogous to that described for Example 53, substituting the appropriate acid for 2-ethoxynaphthoic acid.

TABLE 5 Mol Formula t_(R) [min] MS Data Ex. Name Mol Weight (Methode) m/z [M + H]⁺ 54 [2-(3-methyl-thiophene-2-carbonyl)-1,2,3,4- C19H18N2O3S 2.33 355.23 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 354.43 (LC-2) 55 [2-(5-methyl-thiophene-2-carbonyl)-1,2,3,4- C19H18N2O3S 2.38 355.23 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 354.43 (LC-2) 56 [2-(pyridine-4-carbonyl)-1,2,3,4-tetrahydro- C19H17N3O3 1.90 336.25 pyrido[4,3-b]indol-5-yl]-acetic acid 335.36 (LC-2)

Example 57 (2-Phenylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid (Method E)

Step a): To a stirred solution of Intermediate 1 (20 mg, 0.068 mmol) and DIEA (35 μl, 0.20 mmol) in dichloromethane (1 ml) is added phenyl isocyanate (8.2 μl, 0.075 mmol). The reaction mixture is kept stirring at rt for 1 h, then 1N HCl (2 ml) was added. The aqueous layer is extracted twice with dichloromethane. The organic layers are combined and the solvent is evaporated to give crude ethyl (2-phenylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid: t_(R) (LC-2) 2.23 min; ESI-MS (positive ion): m/z 400.39 [M+Na]⁺ (calcd 377.44 for C₂₂H₂₃N₃O₃); ¹H-NMR (CDCl₃): 1.19 (t, J=7.0 Hz, 3H); 2.77 (t, J=5.3 Hz, 2H); 3.91 (t, J=5.3 Hz, 2H); 4.14 (q, J=7.0 Hz, 2H); 4.65 (s, 2H); 4.68 (s, 2H); 6.46 (s, 1H); 6.98 (t, J=7.0 Hz, 1H); 7.04-7.09 (m, 1H); 7.14-7.16 (m, 2H); 7.20-7.26 (m, 2H); 7.32-7.35 (m, 2H); 7.40 (d, J=7.6 Hz, 1H).

Step b): The title compound is obtained using conditions for the hydrolysis of the above crude analogous to Example 1: t_(R) (LC-2) 1.95 min; ESI-MS (positive ion): m/z 350.26 [M+H]⁺ (calcd 349.39 for C₂₀H₁₉N₃O₃); ¹H-NMR (DMSO-D₆): 2.77 (m, 2H); 3.83 (t, J=5.3 Hz, 2H); 4.67 (s, 2H); 4.91 (s, 2H); 6.91 (t, J=7.0 Hz, 1H); 6.99-7.10 (m, 2H); 7.19-7.24 (m, 2H); 7.35-7.47 (m, 4H); 8.64 (s, 1H); 13.0 (br s, 1H).

Example 58 (2-Ethylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid

The title compound is prepared using a procedure analogous to Example 57, substituting ethyl isocyanate for phenyl isocyanate: t_(R) (LC-2) 1.68 min; ESI-MS (positive ion): m/z 302.24 [M+H]⁺ (calcd 301.35 for C₁₆H₁₉H₃O₃).

Example 59 (2-Phenethyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate, sodium salt (Method F)

Step a): To a stirred solution of Intermediate 1 (50 mg, 0.17 mmol) and DIEA (73 μl, 0.42 mmol) in acetonitrile (1 ml) is added (2-bromo-ethyl)-benzene (26 μl, 0.19 mmol). The reaction mixture is stirred at rt overnight. The solvent is removed under reduced pressure and the crude product is purified by silica gel column chromatography (hexane/EtOAc 3:1, 1% NEt₃), affording pure ethyl (2-phenethyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate (37 mg) in 60% yield: t_(R) (LC-2) 1.69 min; ESI-MS (pos. ion): m/z 363.26 [M+H]⁺ (calcd 362.46 for C₂₃H₂₆N₂O₂).

Step b): A stirred solution of the above ester in THF (1 ml) was treated with 0.2 N aqueous NaOH (0.51 ml, 0.10 mmol) at rt for 15 min. The yellow solution is diluted with 0.5 ml of water and washed twice with diethyl ether (2 ml each). The aqueous phase is concentrated and the precipitate filtered off, affording pure title compound (29 mg) in 79% yield: t_(R) (LC-2) 1.55 min; ESI-MS (pos. ion): m/z 335.36 [M+H]⁺ (calcd 334.41 for C₂₁H₂₂N₂O₂).

Example 60 [2-(3-Phenyl-propyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetate, sodium salt

The title compound is prepared using a procedure analogous to Example 59, substituting (3-bromo-propyl)-benzene for (2-bromo-ethyl)-benzene: t_(R) (LC-2) 1.61 min; ESI-MS (positive ion): m/z 349.37 [M+H]⁺ (calcd 348.44 for C₂₂H₂₄N₂O₂).

Examples 61-67 of the following Table 6 are prepared using a procedure analogous to that described for Example 1, substituting the appropriate substituted (2-tert.-butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate for (2-tert.-butoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetate.

TABLE 6 Mol Formula t_(R) [min] MS Data Ex. Name Mol Weight (Methode) m/z [M + H]⁺ 61 5-carboxymethyl-7-chloro-1,3,4,5-tetrahydro- C18H21N2O4Cl 1.10 363.09 [M − H]⁺ pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester 364.828 (LC-4) 62 5-carboxymethyl-8-chloro-1,3,4,5-tetrahydro- C18H21N2O4Cl 1.10 363.09 [M − H]⁺ pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester 364.828 (LC-4) 63 5-carboxymethyl-6-chloro-1,3,4,5-tetrahydro- C18H21N2O4Cl 1.15 363.09 [M − H]⁺ pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester 364.828 (LC-4) 64 5-carboxymethyl-7-methyl-1,3,4,5-tetrahydro- C19H24N2O4 1.13 343.22 [M − H]⁺ pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester 344.41 (LC-4) 65 5-carboxymethyl-8-methyl-1,3,4,5-tetrahydro- C19H24N2O4 1.14 343.08 [M − H]⁺ pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester 344.41 (LC-4) 66 8-bromo-5-carboxymethyl-1,3,4,5-tetrahydro- C18H21N2O4Br 1.11 410.83 pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester 409.279 (LC-4) 67 5-carboxymethyl-8-fluoro-1,3,4,5-tetrahydro- C18H21N2O4F 1.07 347.17 [M − H]⁺ pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester 348.373 (LC-4)

Examples 68-96 of the following Table 7 are prepared using a procedure analogous to that described for Example 6, substituting the appropriate acid chloride for naphthoylchloride and substituting the appropriate Intermediate for Intermediate 1.

TABLE 7 Mol Formula t_(R) [min] MS Data Ex. Name Mol Weight (Methode) m/z [M + H]⁺ 68 [7-chloro-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro- C20H16N2O3Cl2 1.10 402.87 [M − H]⁺ pyrido[4,3-b]indol-5-yl]-acetic acid 403.264 (LC-4) 69 [8-chloro-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro- C20H16N2O3Cl2 1.10 402.8 [M − H]⁺ pyrido[4,3-b]indol-5-yl]-acetic acid 403.264 (LC-4) 70 [6-chloro-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro- C20H16N2O3Cl2 1.08 402.97 [M − H]⁺ pyrido[4,3-b]indol-5-yl]-acetic acid 403.264 (LC-4) 71 [2-(3-chloro-benzoyl)-7-methyl-1,2,3,4-tetrahydro- C21H19N2O3Cl 1.04 383.10 pyrido[4,3-b]indol-5-yl]-acetic acid 382.846 (LC-4) 72 [2-(3-chloro-benzoyl)-8-methyl-1,2,3,4-tetrahydro- C21H19N2O3Cl 1.07 382.87 [M]⁺ pyrido[4,3-b]indol-5-yl]-acetic acid 382.846 (LC-4) 73 [8-bromo-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro- C20H16N2O3BrCl 1.11 448.83 pyrido[4,3-b]indol-5-yl]-acetic acid 447.715 (LC-4) 74 [2-(3-chloro-benzoyl)-8-fluoro-1,2,3,4-tetrahydro- C20H16N2O3ClF 1.03 385.09 [M − H]⁺ pyrido[4,3-b]indol-5-yl]-acetic acid 386.809 (LC-4) 75 [8-chloro-2-(thiophene-2-carbonyl)-1,2,3,4- C18H15N2O3ClS 1.06 373.05 [M − H]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 374.847 (LC-4) 76 [6-chloro-2-(thiophene-2-carbonyl)-1,2,3,4- C18H15N2O3ClS 1.05 375.06 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 374.847 (LC-4) 77 [8-bromo-2-(thiophene-2-carbonyl)-1,2,3,4- C18H15N2O3BrS 1.08 421.01 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 419.298 (LC-4) 78 [8-fluoro-2-(thiophene-2-carbonyl)-1,2,3,4- C18H15N2O3FS 1.03 359.00 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 358.392 (LC-4) 79 [7-chloro-2-(thiophene-2-carbonyl)-1,2,3,4- C18H15N2O3ClS 1.01 375.00 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 374.847 (LC-4) 80 [7-methyl-2-(thiophene-2-carbonyl)-1,2,3,4- C19H18N2O3S 1.01 355.06 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 354.429 (LC-4) 81 [8-methyl-2-(thiophene-2-carbonyl)-1,2,3,4- C19H18N2O3S 1.04 355.06 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 354.429 (LC-4) 82 [8-fluoro-2-(2-methoxy-naphthalene-1-carbonyl)- C25H21N2O4F 1.04 431.12 [M − H]⁺ 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 432.45 (LC-4) 83 [8-fluoro-2-(4-methoxy-naphthalene-1-carbonyl)- C25H21N2O4F 1.05 431.12 [M − H]⁺ 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 432.45 (LC-4) 84 [8-chloro-2-(2-methoxy-naphthalene-1-carbonyl)- C25H21N2O4Cl 1.07 447.04 [M − H]⁺ 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 448.905 (LC-4) 85 [8-chloro-2-(4-methoxy-naphthalene-1-carbonyl)- C25H21N2O4Cl 1.08 448.82 [M]⁺ 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 448.905 (LC-4) 86 [2-(2-methoxy-naphthalene-1-carbonyl)-8-methyl- C26H24N2O4 1.04 429.04 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 428.487 (LC-4) 87 [2-(4-methoxy-naphthalene-1-carbonyl)-8-methyl- C26H24N2O4 1.08 429.04 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 428.487 (LC-4) 88 [2-(2-methoxy-naphthalene-1-carbonyl)-7-methyl- C26H24N2O4 1.04 429.04 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 428.487 (LC-4) 89 [2-(2-ethoxy-naphthalene-1-carbonyl)-8-methyl- C27H26N2O4 1.07 443.14 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 442.513 (LC-4) 90 [2-(2-ethoxy-naphthalene-1-carbonyl)-7-methyl- C27H26N2O4 1.07 443.14 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 442.513 (LC-4) 91 [2-(4-methoxy-naphthalene-1-carbonyl)-7-methyl- C26H24N2O4 1.06 429.15 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 428.487 (LC-4) 92 [2-(2-fluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3- C20H17N2O3F 0.87 353.18 b]indol-5-yl]-acetic acid 352.364 (LC-5) 93 [2-(3-fluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3- C20H17N2O3F 0.88 353.18 b]indol-5-yl]-acetic acid 352.364 (LC-5) 94 [2-(3,5-difluoro-benzoyl)-1,2,3,4-tetrahydro- C20H16N2O3F2 0.90 371.17 pyrido[4,3-b]indol-5-yl]-acetic acid 370.354 (LC-5) 95 [2-(3,4,5-trifluoro-benzoyl)-1,2,3,4-tetrahydro- C20H15N2O3F3 0.92 389.14 pyrido[4,3-b]indol-5-yl]-acetic acid 388.344 (LC-5) 96 [2-(2,3,4,5-tetrafluoro-benzoyl)-1,2,3,4-tetrahydro- C20H14N2O3F4 0.94 407.13 pyrido[4,3-b]indol-5-yl]-acetic acid 406.334 (LC-5)

Examples 97-106 of the following Table 8 are prepared using a procedure analogous to that described for Example 32, substituting the appropriate Intermediate for Intermediate 1 and the appropriate phenylhydrazine for 4-methoxyphenylhydrazine.

TABLE 8 Mol Formula t_(R) [min] MS Data Ex. Name Mol Weight (Methode) m/z [M + H]⁺ 97 (2-benzoyl-8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3- C20H17N2O3F 1.99 353.13 b]indol-5-yl)-acetic acid 352.364 (LC-6) 98 (2-benzoyl-6-chloro-1,2,3,4-tetrahydro-pyrido[4,3- C20H17N2O3Cl 1.35 369.44 b]indol-5-yl)-acetic acid 368.819 (LC-7) 99 (2-benzoyl-8-isopropyl-1,2,3,4-tetrahydro- C23H24N2O3 1.45 377.51 pyrido[4,3-b]indol-5-yl)-acetic acid 376.455 (LC-7) 100 (2-benzoyl-8-chloro-1,2,3,4-tetrahydro-pyrido[4,3- C20H17N2O3Cl 1.35 369.44 b]indol-5-yl)-acetic acid 368.819 (LC-7) 101 (2-benzoyl-7,8-dichloro-1,2,3,4-tetrahydro- C20H16N2O3Cl2 1.08 402.97 [M − H]⁺ pyrido[4,3-b]indol-5-yl)-acetic acid 403.264 (LC-4) 102 (2-benzoyl-8-trifluoromethyl-1,2,3,4-tetrahydro- C21H17N2O3F3 1.03 403.01 pyrido[4,3-b]indol-5-yl)-acetic acid 402.371 (LC-4) 103 (2-benzoyl-8-tert-butyl-1,2,3,4-tetrahydro-pyrido[4,3- C24H26N2O3 1.07 389.17 [M − H]⁺ b]indol-5-yl)-acetic acid 390.481 (LC-4) 104 (2-benzoyl-7-chloro-8-methyl-1,2,3,4-tetrahydro- C21H19N2O3Cl 1.04 381.14 [M − H]⁺ pyrido[4,3-b]indol-5-yl)-acetic acid 382.846 (LC-4) 105 (2-benzoyl-7,8-dimethyl-1,2,3,4-tetrahydro- C22H22N2O3 1.01 363.09 pyrido[4,3-b]indol-5-yl)-acetic acid 362.428 (LC-4) 106 (2-benzoyl-7-fluoro-1,2,3,4-tetrahydro-pyrido[4,3- C20H17N2O3F 0.97 351.19 [M − H]⁺ b]indol-5-yl)-acetic acid 352.364 (LC-4)

Examples 107-149 of the following Table 9 are prepared using a procedure analogous to that described for Example 53, substituting the appropriate acid for 2-ethoxynaphthoic acid.

TABLE 9 Mol Formula t_(R) [min] MS Data Ex. Name Mol Weight (Methode) m/z [M + H]⁺ 107 [7-chloro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4- C25H21N2O3Cl 1.13 433.03 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 432.906 (LC-4) 108 [8-chloro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4- C25H21N2O3Cl 1.09 431.05 [M − H]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 432.906 (LC-4) 109 [7-methyl-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4- C26H24N2O3 1.11 413.09 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 412.488 (LC-4) 110 [8-bromo-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4- C25H21N2O3Br 1.16 477.01 [M]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 477.357 (LC-4) 111 [2-(4′-ethyl-biphenyl-4-carbonyl)-7-methyl-1,2,3,4- C29H28N2O3 1.25 453.19 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 452.552 (LC-4) 112 [8-bromo-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4- C28H25N2O3Br 1.30 519.06 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 517.422 (LC-4) 113 [2-(4′-ethyl-biphenyl-4-carbonyl)-8-fluoro-1,2,3,4- C28H25N2O3F 1.22 457.14 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 456.516 (LC-4) 114 [6-chloro-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4- C28H25N2O3Cl 1.17 473.14 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 472.971 (LC-4) 115 [7-chloro-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4- C28H25N2O3Cl 1.27 473.14 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 472.971 (LC-4) 116 [8-chloro-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4- C28H25N2O3Cl 1.28 473.07 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 472.971 (LC-4) 117 [2-(4′-ethyl-biphenyl-4-carbonyl)-8-methyl-1,2,3,4- C29H28N2O3 1.25 453.19 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 452.552 (LC-4) 118 [8-methyl-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4- C26H24N2O3 1.08 413.16 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 412.488 (LC-4) 119 [6-chloro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4- C25H21N2O3Cl 1.12 433.03 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 432.906 (LC-4) 120 [8-chloro-2-(naphthalene-1-carbonyl)-1,2,3,4- C24H19N2O3Cl 1.11 419.07 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 418.879 (LC-4) 121 [6-chloro-2-(naphthalene-1-carbonyl)-1,2,3,4- C24H19N2O3Cl 1.09 419.04 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 418.879 (LC-4) 122 [7-methyl-2-(naphthalene-1-carbonyl)-1,2,3,4- C25H22N2O3 0.95 399.25 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 398.461 (LC-5) 123 [8-methyl-2-(naphthalene-1-carbonyl)-1,2,3,4- C25H22N2O3 0.95 399.22 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 398.461 (LC-5) 124 [8-bromo-2-(naphthalene-1-carbonyl)-1,2,3,4- C24H19N2O3Br 1.12 464.96 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 463.33 (LC-4) 125 [8-fluoro-2-(naphthalene-1-carbonyl)-1,2,3,4- C24H19N2O3F 1.08 403.01 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 402.424 (LC-4) 126 [8-fluoro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4- C25H21N2O3F 1.06 415.05 [M − H]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 416.451 (LC-4) 127 [2-(2-bromo-3-methyl-benzoyl)-7-chloro-1,2,3,4- C21H18N2O3BrC 1.11 462.82 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 461.742 (LC-3) 128 [2-(2-bromo-3-methyl-benzoyl)-8-chloro-1,2,3,4- C21H18N2O3BrCl 1.13 462.82 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 461.742 (LC-3) 129 [2-(2-bromo-3-methyl-benzoyl)-6-chloro-1,2,3,4- C21H18N2O3BrCl 1.11 462.82 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 461.742 (LC-3) 130 [2-(2-bromo-3-methyl-benzoyl)-7-methyl-1,2,3,4- C22H21N2O3Br 1.10 442.88 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 441.324 (LC-3) 131 [2-(2-bromo-3-methyl-benzoyl)-8-methyl-1,2,3,4- C22H21N2O3Br 1.10 442.95 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 441.324 (LC-3) 132 [8-bromo-2-(2-bromo-3-methyl-benzoyl)-1,2,3,4- C21H18N2O3Br2 1.15 506.85 [M]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 506.193 (LC-3) 133 [2-(2-bromo-3-methyl-benzoyl)-8-fluoro-1,2,3,4- C21H18N2O3BrF 1.05 446.89 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 445.287 (LC-3) 134 [8-bromo-2-(2-ethoxy-naphthalene-1-carbonyl)- C26H23N2O4Br 1.12 508.79 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic 507.383 (LC-4) acid 135 [2-(2-ethoxy-naphthalene-1-carbonyl)-8-fluoro- C26H23N2O4F 1.06 446.97 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic 446.477 (LC-4) acid 136 [8-chloro-2-(2-ethoxy-naphthalene-1-carbonyl)- C26H23N2O4Cl 1.09 463.04 1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic 462.932 (LC-4) acid 137 [2-(4-methoxy-naphthalene-1-carbonyl)-1,2,3,4- C25H22N2O4 1.04 413.19 [M − H]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 414.46 (LC-4) 138 [2-(5-bromo-naphthalene-1-carbonyl)-1,2,3,4- C24H19N2O3Br 1.06 464.82 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 463.33 (LC-4) 139 [2-(4-methyl-naphthalene-1-carbonyl)-1,2,3,4- C25H22N2O3 1.04 397.13 [M − H]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 398.461 (LC-4) 140 [2-(2-methyl-naphthalene-1-carbonyl)-1,2,3,4- C25H22N2O3 1.03 397.20 [M − H]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 398.461 (LC-4) 141 [2-(biphenyl-3-carbonyl)-1,2,3,4-tetrahydro- C26H22N2O3 1.07 409.17 [M − H]⁺ pyrido[4,3-b]indol-5-yl]-acetic acid 410.472 (LC-4) 142 [2-(4-fluoro-naphthalene-1-carbonyl)-1,2,3,4- C24H19N2O3F 1.04 401.14 [M − H]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 402.424 (LC-4) 143 [2-(2-methoxy-naphthalene-1-carbonyl)-1,2,3,4- C25H22N2O4 1.01 413.19 [M − H]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 414.46 (LC-4) 144 [2-(9-oxo-9H-fluorene-2-carbonyl)-1,2,3,4- C27H20N2O4 1.04 435.20 [M − H]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 436.466 (LC-4) 145 [2-(9H-fluorene-1-carbonyl)-1,2,3,4-tetrahydro- C27H22N2O3 1.07 423.01 pyrido[4,3-b]indol-5-yl]-acetic acid 422.483 (LC-4) 146 [2-(9H-fluorene-4-carbonyl)-1,2,3,4-tetrahydro- C27H22N2O3 1.05 421.21 [M − H]⁺ pyrido[4,3-b]indol-5-yl]-acetic acid 422.483 (LC-4) 147 [2-(2,4,6-trifluoro-benzoyl)-1,2,3,4-tetrahydro- C20H15N2O3F3 0.90 389.1 pyrido[4,3-b]indol-5-yl]-acetic acid 388.344 (LC-5) 148 [2-(4-cyclohexyl-benzoyl)-1,2,3,4-tetrahydro- C26H28N2O3 1.03 417.22 pyrido[4,3-b]indol-5-yl]-acetic acid 416.519 (LC-5) 149 [2-(1H-indole-4-carbonyl)-1,2,3,4-tetrahydro- C22H19N3O3 0.84 374.19 pyrido[4,3-b]indol-5-yl]-acetic acid 373.411 (LC-5)

Examples 150-171 of the following Table 10 are prepared using a procedure analogous to that described for Example 57, substituting the appropriate isocyanate or isothiocyanate, respectively, for phenyl isocyanate.

TABLE 10 Mol Formula t_(R) [min] MS Data Ex. Name Mol Weight (Methode) m/z [M + H]⁺ 150 [2-(2-fluoro-phenylcarbamoyl)-1,2,3,4-tetrahydro- C20H18N3O3F 0.99 368.00 pyrido[4,3-b]indol-5-yl]-acetic acid 367.379 (LC-3) 151 [2-(3-fluoro-phenylcarbamoyl)-1,2,3,4-tetrahydro- C20H18N3O3F 1.02 368.00 pyrido[4,3-b]indol-5-yl]-acetic acid 367.379 (LC-3) 152 [2-(4-fluoro-phenylcarbamoyl)-1,2,3,4-tetrahydro- C20H18N3O3F 1.00 368.07 pyrido[4,3-b]indol-5-yl]-acetic acid 367.379 (LC-3) 153 (2-o-tolylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3- C21H21N3O3 0.99 364.03 b]indol-5-yl)-acetic acid 363.416 (LC-3) 154 (2-m-tolylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3- C21H21N3O3 1.03 364.06 b]indol-5-yl)-acetic acid 363.416 (LC-3) 155 (2-p-tolylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3- C21H21N3O3 1.02 363.57 b]indol-5-yl)-acetic acid 363.416 (LC-3) 156 (2-benzylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3- C21H21N3O3 0.98 364.47 b]indol-5-yl)-acetic acid 363.416 (LC-3) 157 (2-phenethylcarbamoyl-1,2,3,4-tetrahydro- C22H23N3O3 1.00 378.04 pyrido[4,3-b]indol-5-yl)-acetic acid 377.443 (LC-3) 158 [2-(naphthalen-1-ylcarbamoyl)-1,2,3,4-tetrahydro- C24H21N3O3 1.03 399.97 pyrido[4,3-b]indol-5-yl]-acetic acid 399.449 (LC-3) 159 [2-(naphthalen-2-ylcarbamoyl)-1,2,3,4-tetrahydro- C24H21N3O3 1.08 400.14 pyrido[4,3-b]indol-5-yl]-acetic acid 399.449 (LC-3) 160 [2-(biphenyl-2-ylcarbamoyl)-1,2,3,4-tetrahydro- C26H23N3O3 1.09 426.18 pyrido[4,3-b]indol-5-yl]-acetic acid 425.487 (LC-3) 161 (2-cyclohexylcarbamoyl-1,2,3,4-tetrahydro- C20H25N3O3 1.01 356.16 pyrido[4,3-b]indol-5-yl)-acetic acid 355.437 (LC-3) 162 [2-(2-chloro-phenylcarbamoyl)-1,2,3,4-tetrahydro- C20H18N3O3Cl 1.03 383.96 pyrido[4,3-b]indol-5-yl]-acetic acid 383.834 (LC-3) 163 [2-(4-fluoro-phenylthiocarbamoyl)-1,2,3,4- C20H18N3O2FS 1.02 383.91 [M]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 383.446 (LC-4) 164 (2-phenylthiocarbamoyl-1,2,3,4-tetrahydro- C20H19N3O2S 1.01 364.12 [M − H]⁺ pyrido[4,3-b]indol-5-yl)-acetic acid 365.456 (LC-4) 165 (2-phenethylthiocarbamoyl-1,2,3,4-tetrahydro- C22H23N3O2S 1.07 392.08 [M − H]⁺ pyrido[4,3-b]indol-5-yl)-acetic acid 393.51 (LC-4) 166 (2-cyclohexylthiocarbamoyl-1,2,3,4-tetrahydro- C20H25N3O2S 1.07 372.01 pyrido[4,3-b]indol-5-yl)-acetic acid 371.504 (LC-4) 167 (2-benzylthiocarbamoyl-1,2,3,4-tetrahydro- C21H21N3O2S 1.05 378.10 [M − H]⁺ pyrido[4,3-b]indol-5-yl)-acetic acid 379.483 (LC-4) 168 [2-(2-chloro-phenylthiocarbamoyl)-1,2,3,4- C20H18N3O2ClS 1.03 398.10 [M − H]⁺ tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid 399.901 (LC-4) 169 (2-p-tolylthiocarbamoyl-1,2,3,4-tetrahydro- C21H21N3O2S 1.05 378.10 [M − H]⁺ pyrido[4,3-b]indol-5-yl)-acetic acid 379.483 (LC-4) 170 (2-m-tolylthiocarbamoyl-1,2,3,4-tetrahydro- C21H21N3O2S 1.07 380.05 pyrido[4,3-b]indol-5-yl)-acetic acid 379.483 (LC-4) 171 (2-o-tolylthiocarbamoyl-1,2,3,4-tetrahydro- C21H21N3O2S 1.05 378.10 [M − H]⁺ pyrido[4,3-b]indol-5-yl)-acetic acid 379.483 (LC-4)

TABLE 11 NMR data of Intermediates 1-8 are given below. Chemical shifts (δ) in parts per million (ppm), solvent DMSO-d₆ Intermediate 1 1.20 (t, J = 7.0 Hz, 3H); 2.97 (t, J = 5.8 Hz, 2H); 3.45 (t, J = 5.8 Hz, 2H); 4.13 (q, J = 7.0 Hz, 2H); 4.30 (s, 2H); 5.08 (s, 2H); 7.05 (t, J = 7.6 Hz, 1H); 7.14 (t, J = 7.6 Hz, 1H); 7.41 (d, J = 8.2 Hz); 7.48 (d, J = 7.6 Hz, 1H); 9.55 (br s, 2H). Intermediate 2 1.20 (t, J = 7.0 Hz, 3H); 2.97 (ps t, J = 5.8, 5.3 Hz, 2H); 3.43 (ps t, J = 5.3, 4.7 Hz, 2H); 4.13 (q, J = 7.0 Hz, 2H); 4.28 (br s, 2H); 5.10 (s, 2H); 7.25 (dd, J = 8.8, 1.8 Hz, 1H); 7.42 (d, J = 8.8 Hz, 1H); 7.73 (d, J = 1.8 Hz, 1H); 9.61 (br s, 2H). Intermediate 3 1.20 (t, J = 7.0 Hz, 3H); 2.36 (s, 3H); 2.94 (t, J = 5.8 Hz, 2H); 3.44 (m, 2H); 4.12 (q, J = 7.0 Hz, 2H); 4.27 (br s, 2H); 5.03 (s, 2H); 7.00 (dd, J = 8.8, 1.8 Hz, 1H); 7.25-7.30 (m, 2H); 9.45 (br s, 2H). Intermediate 4 1.21 (t, J = 7.0 Hz, 3H); 2.38 (s, 3H); 2.94 (m, 2H); 3.43 (m, 2H); 4.13 (q, J = 7.0 Hz, 2H); 4.27 (br s, 2H); 5.02 (s, 2H); 6.88 (d, J = 8.2 Hz, 1H); 7.20 (s, 1H); 7.35 (d, J = 8.2 Hz, 1H); 9.50 (br s, 2H). Intermediate 5 1.21 (t, J = 7.0 Hz, 3H); 2.95 (t, J = 5.8 Hz, 2H); 3.44 (m, 2H); 4.14 (q, J = 7.0 Hz, 2H); 4.29 (s, 2H); 5.12 (s, 2H); 7.08 (dd, J = 8.2, 1.8 Hz, 1H); 7.50 (d, J = 8.2 Hz, 1H); 7.62 (d, J = 1.8 Hz, 1H); 9.52 (br s, 2H). Intermediate 6 1.20 (t, J = 7.0 Hz, 3H); 2.96 (t, J = 5.8 Hz, 2H); 3.45 (t, J = 5.8 Hz, 2H); 4.13 (q, J = 7.0 Hz, 2H); 4.29 (s, 2H); 5.11 (s, 2H); 7.14 (dd, J = 8.8, 1.8 Hz, 1H); 7.47 (d, J = 8.8 Hz, 1H); 7.60 (d, J = 2.3 Hz, 1H); 9.41 (br s, 2H). Intermediate 7 1.20 (t, J = 7.0 Hz, 3H); 2.98 (t, J = 5.8 Hz, 2H); 3.46 (m, 2H); 4.16 (q, J = 7.0 Hz, 2H); 4.29 (br s, 2H); 5.26 (s, 2H); 7.05 (t, J = 7.6 Hz, 1H); 7.15 (dd, J = 7.6, 1.2 Hz, 1H); 7.48 (dd, J = 7.6, 1.2 Hz, 1H); 9.62 (br s, 2H). Intermediate 8 1.20 (t, J = 7.0 Hz, 3H); 2.96 (ps t, J = 5.8, 5.3 Hz, 2H); 3.44 (m, 2H); 4.13 (q, J = 7.0 Hz, 2H); 4.26 (br s, 2H); 5.09 (s, 2H); 6.97 (td, J = 9.4, 2.3 Hz, 1H); 7.32 (dd, J = 10.0, 2.3 Hz, 1H); 7.41-7.46 (m, 1H); 9.62 (br s, 2H).

TABLE 12 NMR data of selected Examples are given below. Example No. Chemical shifts (δ) in parts per million (ppm), solvent: DMSO-d₆ 1 1.43 (s, 9H); 2.70 (ps t, J = 5.8, 5.3 Hz, 2H); 3.70 (ps t, J = 5.8, 5.3 Hz, 2H); 4.53 (s, 2H); 4.89 (s, 2H); 7.00 (t, J = 7.6 Hz, 1H); 7.07 (td, J = 8.2, 1.2 Hz, 1H); 7.35 (d, J = 8.2 Hz, 1H); 7.40 (d, J = 7.6 Hz, 1H). 8 mixture of rotamers: 2.79 (m, 2H); 3.65/3.99 (m, 2H); 4.59/4.79 (m, 2H); 4.91 (s, 2H); 6.94-7.18 (m, 2H); 7.37 (d, J = 7.6 Hz, 1H); 7.42-7.49 (m, 6H); 13.0 (br s, 1H). 12 mixture of rotamers: 2.84 (m, 2H); 3.96 (ps t, J = 5.3, 5.9 Hz, 2H); 4.83 (br s, 2H); 4.90 (s, 2H); 6.99 (ps t, J = 7.6, 7.0 Hz, 1H); 7.07 (ps t, J = 7.6, 7.0 Hz, 1H); 7.13-7.16 (m, 1H); 7.36 (d, J = 7.6 Hz, 1H); 7.42 (d, J = 7.6 Hz, 1H); 7.53 (d, J = 2.9 Hz, 1H); 7.76 (d, J = 4.7 Hz, 1H); 13.0 (br s, 1H). 39 mixture of rotamers/atropisomers: 2.33/2.36 (s, 3H); 2.58-2.79 (m 2H); 3.46/3.99 (t, J = 5.3 Hz, 2H); 2.30-4.92 (m, 2H); 4.82/4.87 (s, 2H); 6.84-7.17 (m, 3H); 7.26-7.39 (m, 3H); 7.46 (d, J = 7.6 Hz, 1H); 12.9 (br s, 1H). 51 mixture of rotamers/atropisomers: 2.71-2.78 (m, 2H); 3.87-3.96 (m, 2H); 4.31 (s, 2H); 4.69 (s, 1H); 4.88-4.92 (m, 3H); 6.97-7.11 (m, 2H); 7.33-7.51 (m, 6H); 7.76-7.82 (m, 1H); 7.88-7.98 (m, 2H); 13.0 (br s, 1H). 57 2.77 (m, 2H); 3.83 (t, J = 5.3 Hz, 2H); 4.67 (s, 2H); 4.91 (s, 2H); 6.91 (t, J = 7.0 Hz, 1H); 6.99-7.10 (m, 2H); 7.19-7.24 (m, 2H); 7.35-7.47 (m, 4H); 8.64 (s, 1H); 13.0 (br s, 1H). 61 mixture of rotamers: 1.41 (s, 9H); 2.64-2.70 (m, 2H); 3.66-3.69 (m, 2H); 4.51/4.79 (br s, 2H); 4.91 (s, 2H); 7.00 (d, J = 8.8 Hz, 1H); 7.36 (d, J = 8.8 Hz, 1H); 7.54 (s, 1H); 12.9 (br s, 1H). 63 1.42 (s, 9H); 2.69 (t, J = 5.3 Hz, 2H); 3.70 (t, J = 5.3 Hz, 2H); 4.51 (s, 2H); 5.13 (s, 2H); 6.99 (t, J = 7.6 Hz, 1H); 7.09 (d, J = 7.0 Hz, 1H); 7.41 (d, J = 7.6 Hz, 1H); 13.0 (br s, 1H). 64 1.42 (s, 9H); 2.38 (s, 3H); 2.67 (t, J = 5.3 Hz, 2H); 3.69 (t, J = 5.3 Hz, 2H); 4.49 (s, 2H); 4.84 (s, 2H); 6.84 (d, J = 7.6 Hz, 1H); 7.15 (s, 1H); 7.28 (d, J = 7.6 Hz, 1H); 12.9 (br s, 1H). 65 1.42 (s, 9H); 2.67 (t, J = 5.3 Hz, 2H); 3.69 (t, J = 5.3 Hz, 2H); 4.49 (s, 2H); 4.85 (s, 2H); 6.90 (d, J = 8.2 Hz, 1H); 7.18 (s, 1H); 7.23 (d, J = 8.2 Hz, 1H); 12.9 (br s, 1H). 67 1.42 (s, 9H); 2.68 (m, 2H); 3.68 (m, 2H); 4.49 (m, 2H); 4.90 (s, 2H); 6.90 (td, J = 9.3, 2.1 Hz, 1H); 7.22 (dd, J = 9.3, 2.1 Hz, 1H); 7.38 (dd, J = 8.8, 3.9 Hz, 1H); 13.0 (br s, 1H). 68 mixture of rotamers: 2.79 (m, 2H); 3.64/4.01 (m, 2H); 4.56/4.78 (m, 2H); 5.13 (s, 2H); 6.92-7.11 (m, 2H); 7.28-7.57 (m, 5H); 13.1 (br s, 1H). 73 mixture of rotamers (ratio 1.5:1): 2.79 (m, 2H); 3.63/3.98 m, 2H); 4.56/ 4.77 (m, 2H); 4.93 (s, 2H); 7.16-7.22 (m, 1H); 7.36-7.41 (m, 2H); 7.46-7.73 (m, 4H); 13.1 (br s, 1H). 74 2.78 (br s, 2H); 3.63 and 3.99 (m, 2H); 4.54 and 4.76 (m, 2H); 4.92 (s, 2H); 6.92 (m, 1H); 7.36 (m, 3H); 7.51 (m, 3H); 13.02 (s, 1H). 75 mixture of rotamers: 2.83 (m, 2H); 3.95 (t, J = 5.3 Hz, 2H); 4.82 (br s, 2H); 4.93 (s, 2H); 7.07 (dd, J = 8.8, 1.7 Hz, 1H); 7.15 (t, J = 5.3 Hz, 1H); 7.41 (d, J = 8.8 Hz, 1H); 7.53-7.55 (m, 2H); 7.77 (d, J = 5.3 Hz, 1H); 13.0 (br s, 1H). 77 mixture of rotamers: 2.84 (m, 2H); 3.96 (t, J = 5.3 Hz, 2H); 4.84 (br s, 2H); 4.94 (s, 2H); 7.16 (t, J = 4.7 Hz, 1H); 7.19 (d, J = 8.8 Hz, 1H); 7.38 (d, J = 8.8 Hz, 1H); 7.55 (d, J = 2.3 Hz, 1H); 7.70 (s, 1H); 7.78 (d, J = 4.7 Hz, 1H); 13.0 (br s, 1H). 78 2.84 (m, 2H); 3.97 (pst, J = 5.8, 5.3 Hz, 2H); 4.81 (br s, 2H); 4.93 (s, 2H); 6.91 (td, J = 8.8, 2.3 Hz, 1H); 7.16 (t, J = 4.1 Hz, 1H); 7.28 (dd, J = 9.9, 1.8 Hz, 1H); 7.37-7.42 (m, 1H); 7.53 (d, J = 2.9 Hz, 1H); 7.78 (d, J = 4.7 Hz, 1H); 13.0 (br s, 1H). 79 mixture of rotamers: 2.84 (m, 2H); 3.96 (t, J = 5.3 Hz, 2H); 4.83/5.11 (br s, 2H); 4.95 (s, 2H); 7.01 (dd, J = 8.2, 1.7 Hz, 1H); 7.14 td, J = 5.3, 1.7 Hz, 1H); 7.37-7.54 (m, 2H); 7.56 (d, J = 1.7 Hz, 1H); 7.78 (d, J = 5.3 Hz, 1H); 13.0 (br s, 1H). 82 mixture of rotamers/atropisomers: 2.51-2.89 (m, 2H); 3.47/3.96 (m, 2H); 3.73/3.89 (s, 3H); 4.18-4.38 (m, 1H); 4.87-5.01 (m, 3H); 6.79-6.98 (m, 1H); 7.31-7.54 (m, 6H); 7.87-7.94 (m, 1H); 7.99-8.04 (m, 1H); 13.0 (br s, 1H). 107 2.65-7.72 (m, 2H); 3.81-3.90 (m, 2H); 4.25 (s, 2H); 4.63/4.83 (s, 2H); 4.89 (s, 2H); 6.94-7.00 (m, 1H); 7.27-7.46 (m, 5H); 7.52 (d, J = 2.9 Hz, 1H); 7.74 (t, J = 8.8 Hz, 1H); 7.83-7.94 (m, 2H); 13.0 (s br, 1H). 108 mixture of rotamers and atropisomers: 2.51-2.89 (m, 2H); 3.30/3.47 (m, 2H); 3.73/3.89 (s, 3H); 4.18-4.38 (m, 1H); 4.87-5.01 (m, 3H); 6.79-6.98 (m, 1H); 7.31-7.54 (m, 6H); 7.87-7.94 (m, 1H); 7.99-8.04 (m, 1H); 13.0 (br s, 1H). 109 mixture of isomers: 2.36/2.51 (s, 3H); 2.69-2.74 (m, 2H); 3.81-3.92 (m, 2H); 4.28 (s, 2H); 4.65 (s, 1H); 4.83-5.00 (m, 3H); 6.82 (d, J = 8.2 Hz, 1H); 7.13-7.16 (m, 1H); 7.28-7.50 (m, 5H); 7.78 (t, J = 8.2 Hz, 1H); 7.87-7.98 (m, 2H); 12.9 (br s, 1H). 110 mixture of rotamers: 2.71-2.79 (m, 2H); 3.86-3.95 (m, 2H); 4.28/4.30 (s, 2H); 4.67/4.88 (s, 2H); 4.93/4.95 (s, 2H); 7.20 (d, J = 8.0 Hz, 1H); 7.33-7.52 (m, 5H); 7.66 (s, 1H); 7.80 (t, J = 8.0 Hz, 1H); 7.88-7.98 (m, 2H); 13.0 (br s, 1H). 111 mixture of rotamers: 1.19 (t, J = 7.6 Hz, 3H); 3.36 (s, 3H); 2.63 (q, J = 7.6 Hz, 2H); 2.78 (m, 2H); 3.71/3.98 (m, 2H); 4.63-4.75/5.03 (m, 2H); 4.85/ 4.86 (s, 2H); 6.75-6.93/7.36 (m, 2H); 7.15 (s, 1H); 7.30 (d, J = 8.2 Hz, 2H); 7.50 (d, J = 8.2 Hz, 2H); 7.61 (d, J = 8.2 Hz, 2H); 7.72 (d, J = 8.2 Hz, 2H); 13.0 (br s, 1H). 112 mixture of rotamers: 1.20 (t, J = 7.6 Hz, 3H); 2.64 (q, J = 7.6 Hz, 2H); 2.81 (m, 2H); 3.72/3.99 (m, 2H); 4.66-4.81 (m, 2H); 4.94 (s, 2H); 7.20 (br s, 1H); 7.32 (d, J = 8.2 Hz, 2H); 7.38 (d, J = 8.2 Hz, 1H); 7.52 (d, J = 8.2 Hz, 2H); 7.63 (d, J = 8.2 Hz, 2H); 7.73 (d, J = 8.2 Hz, 3H); 13.1 (br s, 1H). 113 mixture of rotamers: 1.18 (t, J = 7.6 Hz, 3H); 2.62 (q, J = 7.6 Hz, 2H); 2.79 (m, 2H); 3.71/3.97 (m, 2H); 4.62-4.74 (m, 2H); 4.91 (s, 2H); 6.86-7.14 (m, 2H); 7.30 (d, J = 8.2 Hz, 2H); 7.35-7.39 (m, 1H); 7.50 (d, J = 8.2 Hz, 2H); 7.61 (d, J = 8.2 Hz, 2H); 7.71 (d, J = 8.2 Hz, 2H); 13.0 (br s, 1H). 114 mixture of rotamers: 1.19 (t, J = 7.6 Hz, 3H); 2.63 (q, J = 7.6 Hz, 2H); 2.82 (m, 2H); 3.69-4.03 (m, 2H); 4.64-4.81 (m, 2H); 5.14 (s, 2H); 6.96-7.14 (m, 2H); 7.31 (d, J = 8.2 Hz, 3H); 7.52 (d, J = 8.2 Hz, 2H); 7.62 (d, J = 8.2 Hz, 2H); 7.72 (d, J = 8.2 Hz, 2H); 13.1 (br s, 1H). 115 mixture of rotamers: 1.20 (t, J = 7.6 Hz, 3H); 2.64 (q, J = 7.6 Hz, 2H); 2.30 (m, 2H); 3.71/3.99 (m, 2H); 4.66-4.79/5.00-5.08 (m, 2H); 4.96 (s, 2H); 6.91-7.08 (m, 1H); 7.32 (d, J = 8.2 Hz, 2H); 7.53-7.41 (m, 1H); 7.52 (d, J = 8.2 Hz, 2H); 7.56 (s, 1H); 7.63 (d, J = 8.2 Hz, 2H); 7.73 (d, J = 8.8 Hz, 2H); 13.0 (br s, 1H). 116 mixture of rotamers: 1.20 (t, J = 7.6 Hz, 3H); 2.64 (q, J = 7.6 Hz, 2H); 2.81 (m, 2H); 3.73/4.00 (m, 2H); 4.67-4.78 (m, 2H); 4.94 (s, 2H); 7.08 (m, 1H); 7.32 (d, J = 8.2 Hz, 2H); 7.42 (d, J = 8.8 Hz, 1H); 7.52 (d, J = 8.2 Hz, 2H); 7.63 (d, J = 8.2 Hz, 2H); 7.73 (d, J = 8.2 Hz, 2H); 13.0 (br s, 1H). 117 mixture of rotamers: 1.20 (t, J = 7.6 Hz, 3H); 2.37 (s, 3H); 2.64 (q, J = 7.6 Hz, 2H); 2.79 (m, 2H); 3.72/4.00 (m, 2H); 4.64-4.77 (m, 2H); 4.86 (s, 2H); 6.90 (m, 1H); 7.03-7.16 (m, 1H); 7.24 (d, J = 8.2 Hz, 1H); 7.32 (d, J = 8.2 Hz, 2H); 7.52 (d, J = 8.2 Hz, 2H); 7.63 (d, J = 8.2 Hz, 2H); 7.73 (d, J = 8.2 Hz, 2H); 13.0 (br s, 1H). 119 mixture of rotamers: 2.71-2.81 (m, 2H); 3.87-3.96 (m, 2H); 4.29/ 4.31 (s, 2H); 4.68/4.87 (br s, 2H); 5.13/5.15 (s, 2H); 6.98/6.99 (t, J = 7.6 Hz, 1H); 7.09/7.10 (d, J = 7.6 Hz, 1H); 7.32-7.52 (m, 5H); 7.79 (t, J = 8.8 Hz, 1H); 7.88-7.98 (m, 2H); 13.1 (br s, 1H). 120 mixture of rotamers/atropisomers: 2.51-2.90 (m, 2H); 3.22-3.47 (m, 2H); 4.01-4.35 (m, 1H); 4.87-5.02 (m, 3H); 6.96-7.13 (m, 1H); 7.34-7.72 (m, 7H); 7.94-8.00 (m, 2H); 13.0 (br s, 1H). 121 mixture of rotamers: 2.41-2.93 (m, 2H); 3.30/3.49 (m, 2H); 4.01-4.37/ 4.89-5.00 (m, 2H); 5.09/5.18 (s, 2H); 6.76/6.82/6.98-7.03 (m, 1H); 7.06/7.14 (d, J = 7.6 Hz, 1H); 7.41-7.60 (m, 5H); 7.68/7.73 (d, J = 8.2 Hz, 1H); 7.97-8.02 (d, J = 7.6 Hz, 2H); 13.1 (br s, 1H). 124 mixture of rotamers/atropisomers: 2.53-2.90 (m, 2H); 3.23-3.47 (m, 2H); 4.01-4.36 (m, 1H); 4.87-5.02 (m, 3H); 7.10/7.21 (dd, J = 8.9, 1.2 Hz, 1H); 7.28-7.77 (m, 7H); 7.95-8.01 (m, 2H); 13.0 (br s, 1H). 128 mixture of rotamers and atropisomers: 2.36/2.40 (s, 3H); 2.65-2.84 (m, 2H); 3.49/4.01 (t, J = 5.9 Hz, 2H); 4.33/4.74 (s, 2H); 4.90/4.94 (s, 2H); 7.02-7.18 (m, 2H); 7.30-7.41 (m, 3H); 7.44/7.60 (s, 1H); 13.0 (br s, 1H). 129 mixture of rotamers and atropisomers: 2.35/2.40 (s, 3H); 2.67-2.74/ 2.81-2.86 (m, 2H); 3.49-3.52/3.95-4.10 (m, 2H); 4.32/4.70/4.76/ 4.89/4.94 (s, 2H); 5.11/5.16 (s, 2H); 6.86-7.21 (m, 3H); 7.30-7.52 (m, 3H); 13.0 (br s, 1H). 130 mixture of rotamers and atropisomers: 2.31/2.33 (s, 3H); 2.36/2.37 (s, 3H); 2.60-2.79 (m, 2H); 3.46/3.99 (t, J = 5.3 Hz, 2H); 4.28-4.90 (m, 2H); 4.79/4.84 (s, 2H); 6.71/6.85 (d, J = 8.2 Hz, 1H); 7.03-7.40 (m, 5H); 12.9 (br s, 1H). 131 mixture of rotamers and atropisomers: 2.26/2.40 (s, 3H); 2.37 (s, 3H); 2.59-2.81 (m, 2H); 3.49/4.02 (m, 2H); 4.30/4.72 (s, 2H); 4.83/4.87 (s, 2H); 6.85-6.97 (m, 1H); 7.08-7.42 (m, 5H); 12.9 (br s, 1H). 132 mixture of rotamers and atropisomers: 2.36/2.40 (s, 3H); 2.63-2.84 (m, 2H); 3.49/4.01 (t, J = 5.3 Hz, 2H); 4.33/4.74 (s, 2H); 4.90/4.94 (s, 2H); 7.02-7.23 (m, 2H); 7.30-7.42 (m, 3H); 7.47/7.74 (d, J = 1.8 Hz, 1H); 13.0 (br s, 1H). 133 mixture of rotamers and atropisomers: 2.33/2.37 (s, 3H); 2.59-2.81 (m, 2H); 3.45-3.49/3.97-4.02 (m, 2H); 4.28-4.84 (m, 2H); 4.87/4.91 (s, 2H); 6.81-6.94 (m, 1H); 7.03-7.40 (m, 5H); 13.0 (br s, 1H). 150 2.77 (t, J = 5.3 Hz, 2H); 3.83 (t, J = 5.3 Hz, 2H); 4.67 (s, 2H); 4.92 (s, 2H); 6.69-7.21 (m, 5H); 7.36-7.45 (m, 3H); 8.44 (s, 1H); 13.0 (br s, 1H). 151 2.77 (t, J = 5.3 Hz, 2H); 3.83 (t, J = 5.3 Hz, 2H); 4.67 (s, 2H); 4.92 (s, 2H); 6.69 (m, 1H); 7.02 (t, J = 7.6 Hz, 1H); 7.09 (t, J = 8.2 Hz, 1H); 7.24 (d, J = 8.2 Hz, 1H); 7.27 (s, 1H); 7.37 (d, J = 7.6 Hz, 1H); 7.41-7.47 (m, 2H); 8.86 (s, 1H); 13.0 (br s, 1H). 152 2.76 (t, J = 4.7 Hz, 2H); 3.83 (t, J = 5.3 Hz, 2H); 4.66 (s, 2H); 4.92 (s, 2H); 6.99-7.11 (m, 4H); 7.36-7.49 (m, 4H); 8.69 (s, 1H); 13.0 (br s, 1H). 153 2.15 (s, 3H); 2.74-2.81 (m, 2H); 3.83 (t, J = 5.3 Hz, 2H); 4.66 (s, 2H); 4.92 (s, 2H); 6.99-7.19 (m, 6H); 7.36-7.42 (m, 2H); 8.18 (s, 1H); 13.0 (br s, 1H). 154 2.18 (s, 3H); 2.71 (t, J = 4.7 Hz, 2H); 3.77 (t, J = 5.3 Hz, 2H); 4.61 (s, 2H); 4.87 (s, 2H); 6.69 (d, J = 7.6 Hz, 1H); 6.95-7.07 (m, 3H); 7.22 (d, J = 8.8 Hz, 1H); 7.24 (s, 1H); 7.32 (d, J = 7.6 Hz, 1H); 7.37 (d, J = 7.6 Hz, 1H); 8.52 (s, 1H); 12.9 (br s, 1H). 155 2.21 (s, 3H); 2.76 (t, J = 5.3 Hz, 2H); 3.82 (t, J = 5.3 Hz, 2H); 4.65 (s, 2H); 4.91 (s, 2H); 6.99-7.11 (m, 4H); 7.33-7.43 (m, 4H); 8.55 (s, 1H); 13.0 (br s, 1H). 156 2.70 (t, J = 5.3 Hz, 2H); 3.74 (t, J = 5.3 Hz, 2H); 4.28 (d, J = 5.3 Hz, 2H); 4.56 (s, 2H); 4.90 (s, 2H); 7.01 (t, J = 7.6 Hz, 1H); 7.08 (t, J = 7.6 Hz, 1H); 7.16-7.31 (m, 6H); 7.36 (d, J = 7.6 Hz, 1H); 7.38 (d, J = 7.6 Hz, 1H); 13.0 (br s, 1H). 159 2.75 (m, 2H); 3.83 (t, J = 5.3 Hz, 2H); 4.68 (s, 2H); 4.88 (s, 2H); 6.96-7.07 (m, 2H); 7.25-7.40 (m, 4H); 7.59 (dd, J = 8.8, 1.8 Hz, 1H); 7.68 (d, J = 8.2 Hz, 1H); 7.73 (d, J = 8.8 Hz, 2H); 7.97 (d, J = 1.8 Hz, 1H); 8.84 (s, 1H); 12.9 (br s, 1H). 162 2.78 (m, 2H); 3.84 (t, J = 5.3 Hz, 2H); 4.68 (s, 2H); 4.92 (s, 2H); 6.99-7.16 (m, 3H); 7.27 (t, J = 7.6 Hz, 1H); 7.36-7.49 (m, 4H); 8.34 (s, 1H); 13.0 (br s, 1H).

Biological Assay: Preparation of CRTH2 Membranes and Radioligand Binding Assay:

Preparation of the membranes and radioligand binding assays are performed according to known procedures, e.g. Sawyer N. et al. (Br. J. Pharmacol., 2002, 137, 1163-1172). A clonal HEK 293 cell line, expressing high level of recombinant hCRTH2 receptor, is selected for the preparation of membranes. Cells are detached from culture plates in 5 ml buffer A per plate (5 mM Tris, 1 mM MgCl₂×6H₂O, 0.1 mM PMSF, 0.1 mM phenanthroline) using a police rubber and transferred into centrifugation tubes and frozen at −80° C. After thawing, the cells are centrifuged at 500 g for 5 min and then resuspended in buffer A. Cells are then fragmented by homogenization with a Polytron homogenizer for 30 s. The membrane fragments are centrifuged at 3000 g for 40 min and resuspended in membranes in buffer 13 (50 mM Tris, 25 mM MgCl₂, 250 mM saccharose, pH 7.4) and aliquots are stored frozen.

Binding assay is performed in a total volume of 250 μl. In each well, 75 μl buffer C (50 mM Tris, 100 mM NaCl, 1 mM EDTA, 0.1% BSA (protease free), 0.01% NaN₃, pH 7.4) is mixed with 50 μl (³H)-PGD₂ (at 2.5 nM (220.000 dpm per well) from Amersham, TRK734), 100 μl CRTH2 membranes to give 80 μg per well and 25 μl of test compound in buffer C containing 1% DMSO. For unspecific binding, PGD2 is added to the reaction mixture at 1 μM final concentration. This binding assay mix is incubated at rt for 90 min and then filtered through a GF/C filter plate. The filter is washed three times with ice cold binding buffer. Then, 40 μl per well Microscint-40 (Packard) are added and the bound radioactivity is quantified by means of Topcount (Packard).

Test for Antagonist Binding to the CRTH2 Receptor:

Compounds of Formula (I) display IC₅₀ values in the range of 0.1 nM to 1 μM, especially in the range of 1 nM to 100 nM. The following Table 13 exemplifies IC₅₀ values of compounds of the present invention.

TABLE 13 Binding CRTH2 Name IC₅₀ [μM] [2-(Naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3- 0.012 b]indol-5-yl]-acetic acid [2-(3-Chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol- 0.015 5-yl]-acetic acid [2-(2-Bromo-3-methyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3- 0.014 b]indol-5-yl]-acetic acid [2-(4′-Ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro- 0.007 pyrido[4,3-b]indol-5-yl]-acetic acid [2-(4′-Ethyl-biphenyl-4-carbonyl)-8-fluoro-1,2,3,4-tetrahydro- 0.001 pyrido[4,3-b]indol-5-yl]-acetic acid (2-Benzoyl-8-trifluoromethyl-1,2,3,4-tetrahydro-pyrido[4,3- 0.001 b]indol-5-yl)-acetic acid [8-Fluoro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro- 0.003 pyrido[4,3-b]indol-5-yl]-acetic acid [8-Bromo-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro- 0.004 pyrido[4,3-b]indol-5-yl]-acetic acid [2-(5-Bromo-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro- 0.012 pyrido[4,3-b]indol-5-yl]-acetic acid

Intracellular Calcium Mobilization Assay (FLIPR):

Cells (HEK-293), stably expressing the hCRTH₂ receptor under the control of the cytomegalovirus promotor from a single insertion of the expression vector pcDNA5 (Invitrogen), are grown to confluency in DMEM (low glucose, Gibco) medium supplemented with 10% fetal calf serum (both Bioconcept, Switzerland) under standard mammalian cell culture conditions (37° C. in a humidified atmosphere of 5% CO₂). Cells are detached from culture dishes using a dissociation buffer (0.02% EDTA in PBS, Gibco) for 1 min, and collected by centrifugation at 200 g at rt for 5 min in assay buffer [equal parts of Hank's BSS (HBSS, Bioconcept) and DMEM (low glucose, without phenol red, Gibco)]. After incubation for 45 min (37° C. and 5% CO₂) in the presence of 1 μM Fluo-4 and 0.04% Pluronic F-127 (both Molecular Probes), 20 mM HEPES (Gibco) in assay buffer, the cells are washed with and resuspended in assay buffer, then seeded onto 384-well FLIPR assay plates (Greiner) at 50,000 cells in 66 μl per well, and sedimented by centrifugation.

Stock solutions of test compounds are made up at a concentration of 10 mM in DMSO, and serially diluted in assay buffer to concentrations required for inhibition dose response curves. Prostaglandin D₂ (Biomol, Plymouth Meeting, Pa.) is used as an agonist.

A FLIPR384 instrument (Molecular Devices) is operated according to the manufacturer's standard instructions, adding 4 μl of test compound dissolved at 10 mM in DMSO and diluted prior to the experiment in assay buffer to obtain the desired final concentration. 10 μl of 80 nM prostaglandin D₂ (Biomol, Plymouth Meeting, Pa.) in assay buffer, supplemented with 0.8% bovine serum albumin (fatty acid content <0.02%, Sigma), is then added to obtain a final concentration of 10 nM and 0.1%, respectively. Changes in fluorescence are monitored before and after the addition of test compounds at λ_(ex)=488 nm and λ_(em)=540 nm. Emission peak values above base level after prostaglandin D₂ addition are exported after base line subtraction. Values are normalized to high-level control (no test compound added) after subtraction of base line value (no prostaglandin D₂ added). The program XL1fit 3.0 (IDBS) is used to fit the data to a single site dose response curve of the equation (A+((B−A)/(1+((C/x)̂D)))) and to calculate the IC₅₀ values.

Antagonist Analysis

Compounds of general Formula (I) antagonize prostaglandin D2 mediated hCRTH2 receptor activity with an IC₅₀ of less than 10 μM, especially less than 300 nM as exemplified in the following Table 14.

TABLE 14 FLIPR CRTH2 IC₅₀ Name [μM] [2-(3,4,5-Trimethoxy-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3- 0.091 b]indol-5-yl]-acetic acid [2-(3-Chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5- 0.174 yl]-acetic acid [2-(4-Bromo-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5- 0.083 yl]-acetic acid [2-(Furan-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5- 0.088 yl]-acetic acid [8-Chloro-2-(2-methoxy-naphthalene-1-carbonyl)-1,2,3,4- 0.003 tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid [8-Bromo-2-(2-bromo-3-methyl-benzoyl)-1,2,3,4-tetrahydro- 0.015 pyrido[4,3-b]indol-5-yl]-acetic acid [2-(1H-Indole-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol- 0.019 5-yl]-acetic acid 5-Carboxymethyl-8-fluoro-1,3,4,5-tetrahydro-pyrido[4,3- 0.022 b]indole-2-carboxylic acid tert-butyl ester [8-Chloro-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro- 0.050 pyrido[4,3-b]indol-5-yl]-acetic acid 

1. A compound of Formula (I)

wherein R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₅-alkoxy, halogen, nitro, cyano or formyl; and R⁵ represents C₁-C₅-alkyl-carbonyl, C₂-C₅-alkenyl-carbonyl, C₁-C₅-alkyl-carbamoyl, aryl-C₁-C₅-alkyl, aryl-carbonyl, aryl-C₁-C₅-alkyl-carbonyl, aryl-C₁-C₅-alkoxy-carbonyl, aryl-carbamoyl, aryl-thiocarbamoyl, aryl-C₁-C₅-alkyl-carbamoyl, aryl-C₁-C₅-alkyl-thiocarbamoyl, cycloalkyl-carbonyl, cycloalkyl-C₁-C₅-alkyl-carbonyl, cycloalkyl-C₁-C₅-alkoxy-carbonyl, cycloalkyl-carbamoyl, heteroaryl-carbonyl, heteroaryl-C₁-C₅-alkyl-carbonyl or heteroaryl-C₁-C₅-alkoxy-carbonyl; or a salt of the compound.
 2. The compound according to claim 1, wherein R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₅-alkoxy, halogen, nitro, cyano or formyl; and R⁵ represents C₁-C₅-alkyl-carbonyl, C₂-C₅-alkenyl-carbonyl, C₁-C₅-alkyl-carbamoyl, aryl-carbonyl, aryl-C₁-C₅-alkyl-carbonyl, aryl-C₁-C₅-alkoxy-carbonyl, aryl-carbamoyl, cycloalkyl-carbonyl, cycloalkyl-C₁-C₅-alkyl-carbonyl, cycloalkyl-C₁-C₅-alkoxy-carbonyl, heteroaryl-carbonyl, heteroaryl-C₁-C₅-alkyl-carbonyl or heteroaryl-C₁-C₅-alkoxy-carbonyl; or a salt of the compound.
 3. The compound according to claim 1, wherein R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₅-alkoxy or halogen; and R⁵ represents C₁-C₅-alkyl-carbonyl, C₂-C₅-alkenyl-carbonyl, C₁-C₅-alkyl-carbamoyl, aryl-carbonyl, aryl-C₁-C₅-alkyl-carbonyl, aryl-C₁-C₅-alkoxy-carbonyl, aryl-carbamoyl, aryl-thiocarbamoyl, aryl-C₁-C₅-alkyl-carbamoyl, aryl-C₁-C₅-alkyl-thiocarbamoyl, cycloalkyl-carbonyl, cycloalkyl-C₁-C₅-alkyl-carbonyl, cycloalkyl-carbamoyl or heteroaryl-carbonyl; or a salt of the compound.
 4. The compound according to any one of claims 1-3, wherein R¹, R², R³ and R⁴ represent hydrogen, or a salt of the compound.
 5. The compound according to claim 1 or 2, wherein R¹, R², R³ and R⁴ independently represent C₁-C₅-alkyl, C₁-C₃-alkoxy, halogen, nitro, cyano or formyl, or a salt of the compound.
 6. The compound according to any one of claims 1-3, wherein one or two substituents selected from R¹, R², R³ and R⁴ independently represent methyl, trifluoromethyl, methoxy, fluoro, chloro or bromo, or a salt of the compound.
 7. The compound according to claim 1, wherein R⁵ is 2 cyclohexyl-2-phenyl-acetyl; 2-naphthalen-1-yl-acetyl; 2-naphthalen-2-yl-acetyl; 3-cyclopentyl-propionyl; 3-phenyl-propionyl; acetyl; diphenylacetyl; hexanoyl; (E)-but-2-enoyl; 9H-fluoren-9-ylmethoxycarbonyl; benzyloxycarbonyl; phenylacetyl; ethylcarbamoyl; 2-bromo-3-methyl-benzoyl; 2-bromo-5-methyl-benzoyl; 2-methoxy-benzoyl; 3,4,5-trimethoxy-benzoyl; 3,5-bis-trifluoromethyl-benzoyl; 3,5-dimethoxy-benzoyl; 3-chloro-benzoyl; 4-bromo-benzoyl; 4-chloro-benzoyl; 4-methoxy-benzoyl; 4-tert.-butyl-benzoyl; 4-trifluoromethoxy-benzoyl; 4-trifluoromethyl-benzoyl; benzoyl; phenylcarbamoyl; 4′-ethyl-biphenyl-4-carbonyl; biphenyl-2-carbonyl; biphenyl-4-carbonyl; 2-methoxy-naphthalene-1-carbonyl; 4-methoxy-naphthalene-1-carbonyl; 2-ethoxy-naphthalene-1-carbonyl; naphthalene-1-carbonyl; cyclohexane-carbonyl; cyclopropane-carbonyl; pyridine-3-carbonyl; 2-chloro-6-methyl-pyridine-4-carbonyl; pyridine-4-carbonyl; furan-2-carbonyl; furan-3-carbonyl; 2-methyl-furan-3-carbonyl; 3-methyl-furan-2-carbonyl; 5-bromo-furan-2-carbonyl; pyrazine-2-carbonyl, benzo[b]thiophene-2-carbonyl; 5-chloro-thiophene-2-carbonyl; 3-methyl-thiophene-2-carbonyl; 5-methyl-thiophene-2-carbonyl; thiophene-2-carbonyl; or thiophene-3-carbonyl, or a salt of the compound.
 8. The compound according to claim 1, wherein R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₃-alkoxy or halogen; and R⁵ represents C₁-C₅-alkyl-carbonyl; C₁-C₅-alkyl-carbamoyl; C₂-C₅-alkenyl-carbonyl; C₃-C₆-cycloalkyl-carbonyl; C₃-C₆-cycloalkyl-C₁-C₃-alkyl-carbonyl; C₃-C₆-cycloalkyl-carbamoyl; C₃-C₆-cycloalkyl-thiocarbamoyl; phenyl-carbonyl or phenyl-C₁-C₃-alkyl-carbonyl, wherein the phenyl moiety of these two groups may be mono-, di-, tri- or tetra-substituted by substituents independently selected from C₁-C₄-alkyl, C₁-C₃-alkoxy, halogen, trifluoromethyl and trifluoromethoxy, mono-substituted by C₃-C₆-cycloalkyl, or mono-substituted by a phenyl group which in turn may be substituted by a C₁-C₃-alkyl or C₁-C₃-alkoxy group; phenyl-C₁-C₃-alkoxy-carbonyl; phenyl-carbamoyl or phenyl-thiocarbamoyl, wherein these two groups are optionally independently mono- or poly-substituted by C₁-C₅-alkyl and/or halogen; phenyl-C₁-C₃-alkyl-carbamoyl; phenyl-C₁-C₃-alkyl-thiocarbamoyl; biphenyl-carbamoyl; naphthyl-carbonyl, naphthyl-C₁-C₃-alkyl-carbonyl or naphthyl-carbamoyl wherein the naphthyl moieties of these three groups are optionally mono- or poly-substituted by substituents independently selected from C₁-C₃-alkyl, C₁-C₃-alkoxy and halogen; fluorenyl-carbonyl, optionally substituted by oxo; fluorenyl-C₁-C₃-alkoxy-carbonyl; or five- to nine-membered heteroaryl-carbonyl groups containing one to three heteroatoms independently selected from oxygen, nitrogen and sulfur, wherein said groups may be substituted by one or two groups independently selected from C₁-C₃-alkyl, C₁-C₃-alkoxy, halogen and trifluoromethyl; or a salt of the compound.
 9. The compound according to claim 1 or 2, wherein R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₅-alkyl, C₁-C₃-alkoxy or halogen; and R⁵ represents C₁-C₅-alkyl-carbonyl; C₂-C₅-alkenyl-carbonyl; C₃-C₆-cycloalkyl-carbonyl; C₃-C₆-cycloalkyl-C₁-C₃-alkyl-carbonyl; C₃-C₆-cycloalkyl-C₁-C₃-alkoxy-carbonyl; phenyl-carbonyl or phenyl-C₁-C₃-alkyl-carbonyl, wherein the phenyl moiety of said groups may be independently mono-, di- or tri-substituted by C₁-C₄-alkyl, C₁-C₃-alkoxy, halogen, trifluoromethyl or trifluoromethoxy, or mono-substituted by a phenyl group which in turn may be substituted by a C₁-C₃-alkyl or C₁-C₃-alkoxy group; naphthyl-carbonyl; fluorenyl-C₁-C₃-alkoxy-carbonyl; or five- or six-membered heteroaryl-carbonyl groups containing one to three heteroatoms independently selected from oxygen, nitrogen and sulfur, wherein said groups may be substituted by one or two groups independently selected from C₁-C₃-alkyl, C₁-C₃-alkoxy, halogen and trifluoromethyl; or a salt of the compound.
 10. The compound according to claim 1, wherein the compound is: (2-benzyloxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-9H-fluoren-9-ylmethoxycarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-acetyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-phenylacetyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; [2-(3,4,5-trimethoxy-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; (2-cyclohexanecarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; [2-(4-methoxy-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(furan-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; (2-cyclopropanecarbonyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; [2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-methoxy-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-trifluoromethyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3,5-bis-trifluoromethyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3-cyclopentyl-propionyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3-phenyl-propionyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-tert.-butyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-trifluoromethoxy-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-((E)-but-2-enoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3,5-dimethoxy-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; (2-diphenylacetyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-hexanoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; [2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-bromo-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(pyridine-3-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; (2-benzoyl-8-methoxy-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-8-bromo-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-6-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; [2-(pyrazine-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-bromo-3-methyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-bromo-5-methyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-chloro-6-methyl-pyridine-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(biphenyl-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(5-bromo-furan-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3-methyl-furan-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-methyl-furan-3-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(benzo[b]thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(5-chloro-thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(furan-3-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-naphthalen-2-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(thiophene-3-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2 (2 cyclohexyl-2-phenyl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; (2-phenylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-ethylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; [2-(2-ethoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3-methyl-thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(5-methyl-thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; or [2-(pyridine-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid or a salt of the compound.
 11. The compound according to claim 10, wherein the compound is: [[2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-bromo-3-methyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; (2-benzoyl-8-bromo-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; [2-(4-bromo-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; or [2-(furan-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; or a salt of the compound.
 12. The compound according to claim 1, wherein the compound is: 5-carboxymethyl-7-chloro-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester; 5-carboxymethyl-8-chloro-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester; 5-carboxymethyl-6-chloro-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester; 5-carboxymethyl-7-methyl-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester; 5-carboxymethyl-8-methyl-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester; 8-bromo-5-carboxymethyl-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester; 5-carboxymethyl-8-fluoro-1,3,4,5-tetrahydro-pyrido[4,3-b]indole-2-carboxylic acid tert-butyl ester; [7-chloro-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-chloro-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [6-chloro-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3-chloro-benzoyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3-chloro-benzoyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-bromo-2-(3-chloro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3-chloro-benzoyl)-8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-chloro-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [6-chloro-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-bromo-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-fluoro-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [7-chloro-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [7-methyl-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-methyl-2-(thiophene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-fluoro-2-(2-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-fluoro-2-(4-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-chloro-2-(2-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-chloro-2-(4-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-methoxy-naphthalene-1-carbonyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-methoxy-naphthalene-1-carbonyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; 2-(2-methoxy-naphthalene-1-carbonyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-ethoxy-naphthalene-1-carbonyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-ethoxy-naphthalene-1-carbonyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-methoxy-naphthalene-1-carbonyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-fluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3-fluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3,5-difluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3,4,5-trifluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2,3,4,5-tetrafluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; (2-benzoyl-8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-6-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-8-isopropyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-8-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-7,8-dichloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-8-trifluoromethyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-8-tert-butyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-7-chloro-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-7,8-dimethyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzoyl-7-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; [7-chloro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-chloro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [7-methyl-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-bromo-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4′-ethyl-biphenyl-4-carbonyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-bromo-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4′-ethyl-biphenyl-4-carbonyl)-8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [6-chloro-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [7-chloro-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-chloro-2-(4′-ethyl-biphenyl-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4′-ethyl-biphenyl-4-carbonyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-methyl-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [6-chloro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-chloro-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [6-chloro-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [7-methyl-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-methyl-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-bromo-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-fluoro-2-(naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-fluoro-2-(2-naphthalen-1-yl-acetyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-bromo-3-methyl-benzoyl)-7-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-bromo-3-methyl-benzoyl)-8-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-bromo-3-methyl-benzoyl)-6-chloro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-bromo-3-methyl-benzoyl)-7-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-bromo-3-methyl-benzoyl)-8-methyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-bromo-2-(2-bromo-3-methyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-bromo-3-methyl-benzoyl)-8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-bromo-2-(2-ethoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-ethoxy-naphthalene-1-carbonyl)-8-fluoro-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [8-chloro-2-(2-ethoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(5-bromo-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-methyl-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-methyl-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(biphenyl-3-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-fluoro-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-methoxy-naphthalene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; 2-(9-oxo-9H-fluorene-2-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(9H-fluorene-1-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(9H-fluorene-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2,4,6-trifluoro-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-cyclohexyl-benzoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(1H-indole-4-carbonyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(2-fluoro-phenylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(3-fluoro-phenylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-fluoro-phenylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; (2-o-tolylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-m-tolylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-p-tolylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-phenethylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; [2-(naphthalen-1-ylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(naphthalen-2-ylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(biphenyl-2-ylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; (2-cyclohexylcarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; [2-(2-chloro-phenylcarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; [2-(4-fluoro-phenylthiocarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; (2-phenylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-phenethylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-cyclohexylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-benzylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; [2-(2-chloro-phenylthiocarbamoyl)-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl]-acetic acid; (2-p-tolylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; (2-m-tolylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; or (2-o-tolylthiocarbamoyl-1,2,3,4-tetrahydro-pyrido[4,3-b]indol-5-yl)-acetic acid; or a salt of the compound.
 13. (canceled)
 14. A pharmaceutical composition comprising at least one compound according to any one of claim 1, 10, or 12 and an inert carrier material and/or adjuvant.
 15. (canceled)
 16. A method of antagonizing prostaglandin D2 mediated hCRTH2 receptor activity comprising administering to a subject in need thereof an effective amount of the compound according to any one of claim 1, 10, or
 12. 17. The method of claim 16, wherein the subject suffers from at least one of allergic asthma, rhinitis, allergic nephritis, conjunctivitis, atopic dermatitis, bronchial asthma, food allergy, anaphylactic shock, urticaria, eczema, itching, Churg-Strauss syndrome, or sinusitis.
 18. The compound according to any one of claims 1-3, wherein R2 is methyl, fluoro, chloro, bromo, and trifluoromethyl; R3 is hydrogen or chloro; and R1 and R4 are both hydrogen; or a salt of the compound. 